wdiff rfc7591v1.txt rfc7591.txt

Internet Engineering Task Force (IETF) J. Richer, Ed.
Request for Comments: 7591
Category: Standards Track M. Jones
ISSN: 2070-1721 Microsoft
J. Bradley
Ping Identity
M. Machulak
Newcastle University
P. Hunt
Oracle Corporation
June
July 2015

OAuth 2.0 Dynamic Client Registration Protocol

Abstract

This specification defines mechanisms for dynamically registering
OAuth 2.0 clients with authorization servers. Registration requests
send a set of desired client metadata values to the authorization
server. The resulting registration responses return a client
identifier to use at the authorization server and the client metadata
values registered for the client. The client can then use this
registration information to communicate with the authorization server
using the OAuth 2.0 protocol. This specification also defines a set
of common client metadata fields and values for clients to use during
registration.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7591.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 4
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 6 7
2. Client Metadata . . . . . . . . . . . . . . . . . . . . . . . 7 8
2.1. Relationship between Grant Types and Response Types . . . 11 12
2.2. Human-Readable Client Metadata . . . . . . . . . . . . . 12 13
2.3. Software Statement . . . . . . . . . . . . . . . . . . . 13 14
3. Client Registration Endpoint . . . . . . . . . . . . . . . . 14 15
3.1. Client Registration Request . . . . . . . . . . . . . . . 15 16
3.1.1. Client Registration Request Using a Software
Statement . . . . . . . . . . . . . . . . . . . . . . 17 18
3.2. Responses . . . . . . . . . . . . . . . . . . . . . . . . 18 19
3.2.1. Client Information Response . . . . . . . . . . . . . 18 19
3.2.2. Client Registration Error Response . . . . . . . . . 20 21
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 23
4.1. OAuth Dynamic Client Registration Metadata Registry . . . 22
4.1.1. Registration Template . . . . . . . . . . . . . . . . 23 24
4.1.2. Initial Registry Contents . . . . . . . . . . . . . . 23 24
4.2. OAuth Token Endpoint Authentication Methods Registry . . 26 27
4.2.1. Registration Template . . . . . . . . . . . . . . . . 26 28
4.2.2. Initial Registry Contents . . . . . . . . . . . . . . 27 28
5. Security Considerations . . . . . . . . . . . . . . . . . . . 27 28
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 30 32
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 33
7.1. Normative References . . . . . . . . . . . . . . . . . . 31 33
7.2. Informative References . . . . . . . . . . . . . . . . . 33 35
Appendix A. Use Cases . . . . . . . . . . . . . . . . . . . . . 34 33
A.1. Open versus Protected Dynamic Client Registration . . . . 34
A.1.1. Open Dynamic Client Registration . . . . . . . . . . 34
A.1.2. Protected Dynamic Client Registration . . . . . . . . 34
A.2. Registration without or with Software Statements . . . . 34
A.2.1. Registration without a Software Statement . . . . . . 34
A.2.2. Registration with a Software Statement . . . . . . . 34
A.3. Registration by the Client or Developer . . . . . . . . . 35 34
A.3.1. Registration by the Client . . . . . . . . . . . . . 35
A.3.2. Registration by the Developer . . . . . . . . . . . . 35
A.4. Client ID per Client Instance or per Client Software . . 35
A.4.1. Client ID per Client Software Instance . . . . . . . 35
A.4.2. Client ID Shared among All Instances of Client
Software . . . . . . . . . . . . . . . . . . . . . . 35
A.5. Stateful or Stateless Registration . . . . . . . . . . . 36 35
A.5.1. Stateful Client Registration . . . . . . . . . . . . 36
A.5.2. Stateless Client Registration . . . . . . . . . . . . 36
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36

1. Introduction

In order for an OAuth 2.0 [RFC6749] client to utilize an OAuth 2.0
authorization server, the client needs specific information to
interact with the server, including an OAuth 2.0 client identifier to
use at that server. This specification describes how an OAuth 2.0
client can be dynamically registered with an authorization server to
obtain this information.

As part of the registration process, this specification also defines
a mechanism for the client to present the authorization server with a
set of metadata, such as a set of valid redirection URIs. This
metadata can either be communicated either in a self-asserted fashion or as
a set of metadata called a software statement, which is digitally
signed or MACed; protected with a Message Authentication Code (MAC); in the
case of a software statement, the issuer is vouching for the validity
of the data about the client.

Traditionally, registration of a client with an authorization server
is performed manually. The mechanisms defined in this specification
can be used either for a client to dynamically register itself with
authorization servers or for a client developer to programmatically
register the client with authorization servers. Multiple
applications using OAuth 2.0 have previously developed mechanisms for
accomplishing such registrations. This specification generalizes the
registration mechanisms defined by "OpenID Connect Dynamic Client
Registration 1.0" [OpenID.Registration] and used by "User Managed
Access (UMA) Profile of OAuth 2.0" [UMA-Core] in a way that is
compatible with both, while being applicable to a wider set of OAuth
2.0 use cases.

1.1. Notational Conventions

The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
document are to be interpreted as described in [RFC2119].

Unless otherwise noted, all the protocol parameter names and values
are case sensitive.

1.2. Terminology

This specification uses the terms "access token", "authorization
code", "authorization endpoint", "authorization grant",
"authorization server", "client", "client identifier", "client
secret", "grant type", "protected resource", "redirection URI",
"refresh token", "resource owner", "resource server", "response
type", and "token endpoint" defined by OAuth 2.0 [RFC6749] and uses
the term "Claim" defined by JSON Web Token (JWT) [RFC7519].

This specification defines the following terms:

Client Software
Software implementing an OAuth 2.0 client.

Client Instance
A deployed instance of a piece of client software.

Client Developer
The person or organization that builds a client software package
and prepares it for distribution. At the time the client is
built, the developer is often not aware of who the deploying
service provider organizations will be. Client developers will
need to use dynamic registration when they are unable to predict
aspects of the software, such as the deployment URLs, at compile
time. For instance, this can occur when the software API
publisher and the deploying organization are not the same.

Client Registration Endpoint
OAuth 2.0 endpoint through which a client can be registered at an
authorization server. The means by which the URL for this
endpoint is obtained are out of scope for this specification.

Initial Access Token
OAuth 2.0 access token optionally issued by an authorization
server to a developer or client and used to authorize calls to the
client registration endpoint. The type and format of this token
are likely service specific and are out of scope for this
specification. The means by which the authorization server issues
this token as well as the means by which the registration endpoint
validates this token are out of scope for this specification. Use
of an initial access token is required when the authorization
server limits the parties that can register a client.

Deployment Organization
An administrative security domain under which a software API
(service) is deployed and protected by an OAuth 2.0 framework. In
some OAuth scenarios, the deployment organization and the software
API publisher are the same. In these cases, the deploying
organization will often have a close relationship with client
software developers. In many other cases, the definer of the
service may be an independent third-party publisher or a standards
organization. When working to a published specification for an
API, the client software developer is unable to have a prior
relationship with the potentially many deployment organizations
deploying the software API (service).

Software API Deployment
A deployed instance of a software API that is protected by OAuth
2.0 (a protected resource) in a particular deployment organization
domain. For any particular software API, there may be one or more
deployments. A software API deployment typically has an
associated OAuth 2.0 authorization server as well as a client
registration endpoint. The means by which endpoints are obtained
are out of scope for this specification.

Software API Publisher
The organization that defines a particular web-accessible API that
may be deployed in one or more deployment environments. A
publisher may be any standards body, commercial, public, private,
or open source organization that is responsible for publishing and
distributing software and API specifications that may be protected
via OAuth 2.0. In some cases, a software API publisher and a
client developer may be the same organization. At the time of
publication of a web-accessible API, the software publisher often
does not have a prior relationship with the deploying
organizations.

Software Statement
A digitally signed or MACed JSON Web Token (JWT) [RFC7519] that
asserts metadata values about the client software. In some cases,
a software statement will be issued directly by the client
developer. In other cases, a software statement will be issued by
a third-party organization for use by the client developer. In
both cases, the trust relationship the authorization server has
with the issuer of the software statement is intended to be used
as an input to the evaluation of whether the registration request
is accepted. A software statement can be presented to an
authorization server as part of a client registration request.

1.3. Protocol Flow

+--------(A)- Initial Access Token (OPTIONAL)
|
| +----(B)- Software Statement (OPTIONAL)
| |
v v
+-----------+ +---------------+
| |--(C)- Client Registration Request -->| Client |
| Client or | | Registration |
| Developer |<-(D)- Client Information Response ---| Endpoint |
| | or Client Error Response +---------------+
+-----------+

Figure 1: Abstract Dynamic Client Registration Flow

The abstract OAuth 2.0 client dynamic registration flow illustrated
in Figure 1 describes the interaction between the client or developer
and the endpoint defined in this specification. This figure does not
demonstrate error conditions. This flow includes the following
steps:

(A) Optionally, the client or developer is issued an initial access
token giving access to the client registration endpoint. The
method by which the initial access token is issued to the
client or developer is out of scope for this specification.

(B) Optionally, the client or developer is issued a software
statement for use with the client registration endpoint. The
method by which the software statement is issued to the client
or developer is out of scope for this specification.

(C) The client or developer calls the client registration endpoint
with the client's desired registration metadata, optionally
including the initial access token from (A) if one is required
by the authorization server.

(D) The authorization server registers the client and returns:

* the client's registered metadata,

* a client identifier that is unique at the server, and

* a set of client credentials such as a client secret, if
applicable for this client.

Examples of different configurations and usages are included in
Appendix A.

2. Client Metadata

Registered clients have a set of metadata values associated with
their client identifier at an authorization server, such as the list
of valid redirection URIs or a display name.

These client metadata values are used in two ways:

o as input values to registration requests, and

o as output values in registration responses.

The following client metadata fields are defined by this
specification. The implementation and use of all client metadata
fields is OPTIONAL, unless stated otherwise. All data member types
(strings, arrays, numbers) are defined in terms of their JSON
[RFC7159] representations.

redirect_uris
Array of redirection URI strings for use in redirect-based flows
such as the authorization code and implicit flows. As required by
Section 2 of OAuth 2.0 [RFC6749], clients using flows with
redirection MUST register their redirection URI values.
Authorization servers that support dynamic registration for
redirect-based flows MUST implement support for this metadata
value.

token_endpoint_auth_method
String indicator of the requested authentication method for the
token endpoint. Values defined by this specification are:

* "none": The client is a public client as defined in OAuth 2.0 2.0,
Section 2.1, and does not have a client secret.

* "client_secret_post": The client uses the HTTP POST parameters
as defined in OAuth 2.0, Section 2.3.1.

* "client_secret_basic": The client uses HTTP Basic as defined in
OAuth 2.0, Section 2.3.1.

Additional values can be defined via the IANA OAuth "OAuth Token
Endpoint Authentication Methods Registry Methods" registry established in
Section 4.2. Absolute URIs can also be used as values for this
parameter without being registered. If unspecified or omitted,
the default is "client_secret_basic", denoting the HTTP Basic
authentication scheme as specified in Section 2.3.1 of OAuth 2.0.

grant_types
Array of OAuth 2.0 grant type strings that the client can use at
the token endpoint. These grant types are defined as follows:

* "authorization_code": The Authorization Code Grant described authorization code grant type defined
in OAuth 2.0, Section 4.1.

* "implicit": The Implicit Grant described implicit grant type defined in OAuth 2.0,
Section 4.2.

* "password": The Resource Owner Password Credentials Grant
described resource owner password credentials grant type
defined in OAuth 2.0, Section 4.3.

* "client_credentials": The Client Credentials Grant described client credentials grant type defined
in OAuth 2.0, Section 4.4.

* "refresh_token": The Refresh Token Grant described refresh token grant type defined in OAuth
2.0, Section 6.

* "urn:ietf:params:oauth:grant-type:jwt-bearer": The JWT Bearer
Token Grant Type defined in OAuth JWT Bearer Token Profiles
[RFC7523].

* "urn:ietf:params:oauth:grant-type:saml2-bearer": The SAML 2 2.0
Bearer Assertion Grant defined in OAuth SAML 2 Bearer Token
Profiles [RFC7522].

If the token endpoint is used in the grant type, the value of this
parameter MUST be the same as the value of the "grant_type"
parameter passed to the token endpoint defined in the grant type
definition. Authorization servers MAY allow for other values as
defined in the grant type extension process described in OAuth
2.0, Section 2.5. 4.5. If omitted, the default behavior is that the
client will use only the "authorization_code" Grant Type.

response_types
Array of the OAuth 2.0 response type strings that the client can
use at the authorization endpoint. These response types are
defined as follows:

* "code": The authorization code response described type defined in OAuth
2.0, Section 4.1.

* "token": The implicit response described type defined in OAuth 2.0,
Section 4.2.

If the authorization endpoint is used by the grant type, the value
of this parameter MUST be the same as the value of the
"response_type" parameter passed to the authorization endpoint
defined in the grant type definition. Authorization servers MAY
allow for other values as defined in the grant type extension
process is described in OAuth 2.0, Section 2.5. 4.5. If omitted, the
default is that the client will use only the "code" response type.

client_name
Human-readable string name of the client to be presented to the
end-user during authorization. If omitted, the authorization
server MAY display the raw "client_id" value to the end-user
instead. It is RECOMMENDED that clients always send this field.
The value of this field MAY be internationalized, as described in
Section 2.2.

client_uri
URL string of a web page providing information about the client.
If present, the server SHOULD display this URL to the end-user in
a clickable fashion. It is RECOMMENDED that clients always send
this field. The value of this field MUST point to a valid web
page. The value of this field MAY be internationalized, as
described in Section 2.2.

logo_uri
URL string that references a logo for the client. If present, the
server SHOULD display this image to the end-user during approval.
The value of this field MUST point to a valid image file. The
value of this field MAY be internationalized, as described in
Section 2.2.

scope
String containing a space-separated list of scope values (as
described in Section 3.3 of OAuth 2.0 [RFC6749]) that the client
can use when requesting access tokens. The semantics of values in
this list are service specific. If omitted, an authorization
server MAY register a client with a default set of scopes.

contacts
Array of strings representing ways to contact people responsible
for this client, typically email addresses. The authorization
server MAY make these contact addresses available to end-users for
support requests for the client. See Section 6 for information on
Privacy Considerations.

tos_uri
URL string that points to a human-readable terms of service
document for the client that describes a contractual relationship
between the end-user and the client that the end-user accepts when
authorizing the client. The authorization server SHOULD display
this URL to the end-user if it is provided. The value of this
field MUST point to a valid web page. The value of this field MAY
be internationalized, as described in Section 2.2.

policy_uri
URL string that points to a human-readable privacy policy document
that describes how the deployment organization collects, uses,
retains, and discloses personal data. The authorization server
SHOULD display this URL to the end-user if it is provided. The
value of this field MUST point to a valid web page. The value of
this field MAY be internationalized, as described in Section 2.2.

jwks_uri
URL string referencing the client's JSON Web Key (JWK) Set
[RFC7517] document, which contains the client's public keys. The
value of this field MUST point to a valid JWK Set document. These
keys can be used by higher-level protocols that use signing or
encryption. For instance, these keys might be used by some
applications for validating signed requests made to the token
endpoint when using JWTs for client authentication [RFC7523]. Use
of this parameter is preferred over the "jwks" parameter, as it
allows for easier key rotation. The "jwks_uri" and "jwks"
parameters MUST NOT both be present in the same request or
response.

jwks
Client's JSON Web Key Set [RFC7517] document value, which contains
the client's public keys. The value of this field MUST be a JSON
object containing a valid JWK Set. These keys can be used by
higher-level protocols that use signing or encryption. This
parameter is intended to be used by clients that cannot use the
"jwks_uri" parameter, such as native clients that cannot host
public URLs. The "jwks_uri" and "jwks" parameters MUST NOT both
be present in the same request or response.

software_id
A unique identifier string (e.g., a Universally Unique Identifier
(UUID)) assigned by the client developer or software publisher
used by registration endpoints to identify the client software to
be dynamically registered. Unlike "client_id", which is issued by
the authorization server and SHOULD vary between instances, the
"software_id" SHOULD remain the same for all instances of the
client software. The "software_id" SHOULD remain the same across
multiple updates or versions of the same piece of software. The
value of this field is not intended to be human readable and is
usually opaque to the client and authorization server.

software_version
A version identifier string for the client software identified by
"software_id". The value of the "software_version" SHOULD change
on any update to the client software identified by the same
"software_id". The value of this field is intended to be compared
using string equality matching and no other comparison semantics
are defined by this specification. The value of this field is
outside the scope of this specification, but it is not intended to
be human readable and is usually opaque to the client and
authorization server. The definition of what constitutes an
update to client software that would trigger a change to this
value is specific to the software itself and is outside the scope
of this specification.

Extensions and profiles of this specification can expand this list
with metadata names and descriptions registered in accordance with
the IANA Considerations in Section 4 of this document. The
authorization server MUST ignore any client metadata sent by the
client that it does not understand (for instance, by silently
removing unknown metadata from the client's registration record
during processing). The authorization server MAY reject any
requested client metadata values by replacing requested values with
suitable defaults as described in Section 3.2.1 or by returning an
error response as described in Section 3.2.2.

Client metadata values can be either communicated directly in the
body of a registration request, as described in Section 3.1, or
included as claims in a software statement, as described in
Section 2.3; a mixture of both is also possible. If the same client
metadata name is present in both locations and the software statement
is trusted by the authorization server, the value of a claim in the
software statement MUST take precedence.

2.1. Relationship between Grant Types and Response Types

The "grant_types" and "response_types" values described above are
partially orthogonal, as they refer to arguments passed to different
endpoints in the OAuth protocol. However, they are related in that
the "grant_types" available to a client influence the
"response_types" that the client is allowed to use, and vice versa.
For instance, a "grant_types" value that includes
"authorization_code" implies a "response_types" value that includes
"code", as both values are defined as part of the OAuth 2.0
authorization code grant. As such, a server supporting these fields
SHOULD take steps to ensure that a client cannot register itself into
an inconsistent state, for example, by returning an
"invalid_client_metadata" error response to an inconsistent
registration request.

The correlation between the two fields is listed in the table below.

Extensions and profiles of this document that introduce new values to
either the "grant_types" or "response_types" parameter MUST document
all correspondences between these two parameter types.

2.2. Human-Readable Client Metadata

Human-readable client metadata values and client metadata values that
reference human-readable values MAY be represented in multiple
languages and scripts. For example, the values of fields such as
"client_name", "tos_uri", "policy_uri", "logo_uri", and "client_uri"
might have multiple locale-specific values in some client
registrations to facilitate use in different locations.

To specify the languages and scripts, BCP 47 [RFC5646] language tags
are added to client metadata member names, delimited by a "#"
character. Since JSON [RFC7159] member names are case sensitive, it
is RECOMMENDED that language tag values used in Claim Names be
spelled using the character case with which they are registered in
the IANA "IANA Language Subtag Registry Subtag" registry [IANA.Language]. In particular,
normally language names are spelled with lowercase characters, region
names are spelled with uppercase characters, and languages are
spelled with mixed-case characters. However, since BCP 47 language
tag values are case-insensitive, implementations SHOULD interpret the
language tag values supplied in a case insensitive manner. Per the
recommendations in BCP 47, language tag values used in metadata
member names should only be as specific as necessary. For instance,
using "fr" might be sufficient in many contexts, rather than "fr-CA"
or "fr-FR".

For example, a client could represent its name in English as
""client_name#en":
"client_name#en": "My Client"" Client" and its name in Japanese as
""client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D""
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D" within the same
registration request. The authorization server MAY display any or
all of these names to the resource owner during the authorization
step, choosing which name to display based on system configuration,
user preferences or other factors.

If any human-readable field is sent without a language tag, parties
using it MUST NOT make any assumptions about the language, character
set, or script of the string value, and the string value MUST be used
as is wherever it is presented in a user interface. To facilitate
interoperability, it is RECOMMENDED that clients and servers use a
human-readable field without any language tags in addition to any
language-specific fields, and it is RECOMMENDED that any human-
readable fields sent without language tags contain values suitable
for display on a wide variety of systems.

Implementer's Note: Many JSON libraries make it possible to reference
members of a JSON object as members of an object construct in the
native programming environment of the library. However, while the
"#" character is a valid character inside of a JSON object's member
names, it is not a valid character for use in an object member name
in many programming environments. Therefore, implementations will
need to use alternative access forms for these claims. For instance,
in JavaScript, if one parses the JSON as follows, "var j =
JSON.parse(json);", then as a workaround the member "client_name#en-
us" can be accessed using the JavaScript syntax "j["client_name#en-
us"]".

2.3. Software Statement

A software statement is a JSON Web Token (JWT) [RFC7519] that asserts
metadata values about the client software as a bundle. A set of
claims that can be used in a software statement are defined in
Section 2. When presented to the authorization server as part of a
client registration request, the software statement MUST be digitally
signed or MACed using JSON Web Signature (JWS) [RFC7515] and MUST
contain an "iss" (issuer) claim denoting the party attesting to the
claims in the software statement. It is RECOMMENDED that software
statements be digitally signed using the "RS256" signature algorithm,
although particular applications MAY specify the use of different
algorithms. It is RECOMMENDED that software statements contain the
"software_id" claim to allow authorization servers to correlate
different instances of software using the same software statement.

For example, a software statement could contain the following claims:

{
"software_id": "4NRB1-0XZABZI9E6-5SM3R",
"client_name": "Example Statement-based Client",
"client_uri": "https://client.example.net/"
}

The following non-normative example JWT includes these claims and has
been asymmetrically signed using RS256:

Line "RS256" (with line breaks are for
display purposes only only):

eyJhbGciOiJSUzI1NiJ9.
eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll
bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs
aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ.
GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa
zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0
5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY
fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk
U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf
IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA

The software statement is typically distributed with all instances of
a client application. The means by which a client or developer
obtains a software statement are outside the scope of this
specification. Some common methods could include a client developer
generating a client-specific JWT by registering with a software API
publisher to obtain a software statement for a class of clients.

The software statement is
typically distributed with all instances of a client application.

The criteria by which authorization servers determine whether to
trust and utilize the information in a software statement are beyond outside
the scope of this specification.

In some cases, authorization servers MAY choose to accept a software
statement value directly as a client identifier in an authorization
request, without a prior dynamic client registration having been
performed. The circumstances under which an authorization server
would do so, and the specific software statement characteristics
required in this case, are beyond outside the scope of this specification.

3. Client Registration Endpoint

The client registration endpoint is an OAuth 2.0 endpoint defined in
this document that is designed to allow a client to be registered
with the authorization server. The client registration endpoint MUST
accept HTTP POST messages with request parameters encoded in the
entity body using the "application/json" format. The client
registration endpoint MUST be protected by a TLS transport-layer security
mechanism, as described in Section 5.

The client registration endpoint MAY be an OAuth 2.0 [RFC6749]
protected resource and it MAY accept an initial access token in the
form of an OAuth 2.0 access token to limit registration to only
previously authorized parties. The method by which the initial
access token is obtained by the client or developer is generally out
of band and is out of scope for this specification. The method by
which the initial access token is verified and validated by the
client registration endpoint is out of scope for this specification.

To support open registration and facilitate wider interoperability,
the client registration endpoint SHOULD allow registration requests
with no authorization (which is to say, with no initial access token
in the request). These requests MAY be rate-limited or otherwise
limited to prevent a denial-of-service attack on the client
registration endpoint.

3.1. Client Registration Request

This operation registers a client with the authorization server. The
authorization server assigns this client a unique client identifier,
optionally assigns a client secret, and associates the metadata
provided in the request with the issued client identifier. The
request includes any client metadata parameters being specified for
the client during the registration. The authorization server MAY
provision default values for any items omitted in the client
metadata.

To register, the client or developer sends an HTTP POST to the client
registration endpoint with a content type of "application/json". The
HTTP Entity Payload is a JSON [RFC7159] document consisting of a JSON
object and all requested client metadata values as top-level members
of that JSON object.

For example, if the server supports open registration (with no
initial access token), the client could send the following
registration request to the client registration endpoint: endpoint.

The following is a non-normative example request not using an initial
access token (with line wraps within values for display purposes
only): token:

POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Host: server.example.com

{
"redirect_uris":[
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"],
"client_name":"My
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method":"client_secret_basic",
"logo_uri":"https://client.example.org/logo.png",
"jwks_uri":"https://client.example.org/my_public_keys.jwks",
"token_endpoint_auth_method": "client_secret_basic",
"logo_uri": "https://client.example.org/logo.png",
"jwks_uri": "https://client.example.org/my_public_keys.jwks",
"example_extension_parameter": "example_value"
}

Alternatively, if the server supports authorized registration, the
developer or the client will be provisioned with an initial access
token. (The method by which the initial access token is obtained is
out of scope for this specification.) The developer or client sends
the following authorized registration request to the client
registration endpoint. Note that the initial access token sent in
this example as an OAuth 2.0 Bearer Token [RFC6750], but any OAuth
2.0 token type could be used by an authorization server.

The following is a non-normative example request using an initial
access token and registering a JWK Set by value (with line wraps breaks
within values for display purposes only):

POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Authorization: Bearer ey23f2.adfj230.af32-developer321
Host: server.example.com

{
"redirect_uris":["https://client.example.org/callback",
"redirect_uris": ["https://client.example.org/callback",
"https://client.example.org/callback2"],
"client_name":"My
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method":"client_secret_basic",
"policy_uri":"https://client.example.org/policy.html",
"jwks":{"keys":[{
"token_endpoint_auth_method": "client_secret_basic",
"policy_uri": "https://client.example.org/policy.html",
"jwks": {"keys": [{
"e": "AQAB",
"n": "nj3YJwsLUFl9BmpAbkOswCNVx17Eh9wMO-_AReZwBqfaWFcfG
HrZXsIV2VMCNVNU8Tpb4obUaSXcRcQ-VMsfQPJm9IzgtRdAY8NN8Xb7PEcYyk
lBjvTtuPbpzIaqyiUepzUXNDFuAOOkrIol3WmflPUUgMKULBN0EUd1fpOD70p
RM0rlp_gg_WNUKoW1V-3keYUJoXH9NztEDm_D2MQXj9eGOJJ8yPgGL8PAZMLe
2R7jb9TxOCPDED7tY_TU4nFPlxptw59A42mldEmViXsKQt60s1SLboazxFKve
qXC_jpLUt22OC6GUG63p-REw-ZOr3r845z50wMuzifQrMI9bQ",
"kty": "RSA"
}]},
"example_extension_parameter": "example_value"
}

3.1.1. Client Registration Request Using a Software Statement

In addition to JSON elements, client metadata values MAY also be
provided in a software statement, as described in Section 2.3. The
authorization server MAY ignore the software statement if it does not
support this feature. If the server supports software statements,
client metadata values conveyed in the software statement MUST take
precedence over those conveyed using plain JSON elements.

Software statements are included in the requesting JSON object using
this OPTIONAL member:

software_statement
A software statement containing client metadata values about the
client software as claims. This is a string value containing the
entire signed JWT.

In the following example, some registration parameters are conveyed
as claims in a software statement from the example in Section 2.3,
while some values specific to the client instance are conveyed as
regular parameters (with line wraps breaks within values for display
purposes only):

POST /register HTTP/1.1
Content-Type: application/json
Accept: application/json
Host: server.example.com

{
"redirect_uris":[
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"
],
"software_statement":"eyJhbGciOiJSUzI1NiJ9.
"software_statement": "eyJhbGciOiJSUzI1NiJ9.
eyJzb2Z0d2FyZV9pZCI6IjROUkIxLTBYWkFCWkk5RTYtNVNNM1IiLCJjbGll
bnRfbmFtZSI6IkV4YW1wbGUgU3RhdGVtZW50LWJhc2VkIENsaWVudCIsImNs
aWVudF91cmkiOiJodHRwczovL2NsaWVudC5leGFtcGxlLm5ldC8ifQ.
GHfL4QNIrQwL18BSRdE595T9jbzqa06R9BT8w409x9oIcKaZo_mt15riEXHa
zdISUvDIZhtiyNrSHQ8K4TvqWxH6uJgcmoodZdPwmWRIEYbQDLqPNxREtYn0
5X3AR7ia4FRjQ2ojZjk5fJqJdQ-JcfxyhK-P8BAWBd6I2LLA77IG32xtbhxY
fHX7VhuU5ProJO8uvu3Ayv4XRhLZJY4yKfmyjiiKiPNe-Ia4SMy_d_QSWxsk
U5XIQl5Sa2YRPMbDRXttm2TfnZM1xx70DoYi8g6czz-CPGRi4SW_S2RKHIJf
IjoI3zTJ0Y2oe0_EJAiXbL6OyF9S5tKxDXV8JIndSA",
"scope":"read
"scope": "read write",
"example_extension_parameter":"example_value"
"example_extension_parameter": "example_value"
}

3.2. Responses

Upon a successful registration request, the authorization server
returns a client identifier for the client. The server responds with
an HTTP 201 Created status code and a body of type "application/json"
with content as described in Section 3.2.1.

Upon an unsuccessful registration request, the authorization server
responds with an error, as described in Section 3.2.2.

3.2.1. Client Information Response

The response contains the client identifier as well as the client
secret, if the client is a confidential client. The response MAY
contain additional fields as specified by extensions to this
specification.

client_id
REQUIRED. OAuth 2.0 client identifier string. It SHOULD NOT be
currently valid for any other registered client, though an
authorization server MAY issue the same client identifier to
multiple instances of a registered client at its discretion.

client_secret
OPTIONAL. OAuth 2.0 client secret string. If issued, this MUST
be unique for each "client_id" and SHOULD be unique for multiple
instances of a client using the same "client_id". This value is
used by confidential clients to authenticate to the token endpoint
endpoint, as described in OAuth 2.0 [RFC6749], Section 2.3.1.

client_id_issued_at
OPTIONAL. Time at which the client identifier was issued. The
time is represented as the number of seconds from
1970-01-01T0:0:0Z
1970-01-01T00:00:00Z as measured in UTC until the date/time of
issuance.

client_secret_expires_at
REQUIRED if "client_secret" is issued. Time at which the client
secret will expire or 0 if it will not expire. The time is
represented as the number of seconds from 1970-01-01T0:0:0Z 1970-01-01T00:00:00Z as
measured in UTC until the date/time of expiration.

Additionally, the authorization server MUST return all registered
metadata about this client, including any fields provisioned by the
authorization server itself. The authorization server MAY reject or
replace any of the client's requested metadata values submitted
during the registration and substitute them with suitable values.
The client or developer can check the values in the response to
determine if the registration is sufficient for use (e.g., the
registered "token_endpoint_auth_method" is supported by the client
software) and determine a course of action appropriate for the client
software. The response to such a situation is out of scope for this
specification but could include filing a report with the application
developer or authorization server provider, attempted re-registration
with different metadata values, or various other methods. For
instance, if the server also supports a registration management
mechanism such as that defined in [RFC7592], the client or developer
could attempt to update the registration with different metadata
values. This process could also be aided by a service discovery
protocol, such as [OpenID.Discovery], which can list a server's
capabilities, allowing a client to make a more informed registration
request. The use of any such management or discovery system is
optional and outside the scope of this specification.

The successful registration response uses an HTTP 201 Created status
code with a body of type "application/json" consisting of a single
JSON object [RFC7159] with all parameters as top-level members of the
object.

If a software statement was used as part of the registration, its
value MUST be returned unmodified in the response along with other
metadata using the "software_statement" member name. Client metadata
elements used from the software statement MUST also be returned
directly as top-level client metadata values in the registration
response (possibly with different values, since the values requested
and the values used may differ).

The following is a non-normative example response of a successful
registration:

HTTP/1.1 201 Created
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache

{
"client_id":"s6BhdRkqt3",
"client_id": "s6BhdRkqt3",
"client_secret": "cf136dc3c1fc93f31185e5885805d",
"client_id_issued_at":2893256800,
"client_secret_expires_at":2893276800,
"redirect_uris":[
"client_id_issued_at": 2893256800,
"client_secret_expires_at": 2893276800,
"redirect_uris": [
"https://client.example.org/callback",
"https://client.example.org/callback2"],
"grant_types": ["authorization_code", "refresh_token"],
"client_name":"My
"client_name": "My Example Client",
"client_name#ja-Jpan-JP":
"\u30AF\u30E9\u30A4\u30A2\u30F3\u30C8\u540D",
"token_endpoint_auth_method":"client_secret_basic",
"logo_uri":"https://client.example.org/logo.png",
"jwks_uri":"https://client.example.org/my_public_keys.jwks",
"token_endpoint_auth_method": "client_secret_basic",
"logo_uri": "https://client.example.org/logo.png",
"jwks_uri": "https://client.example.org/my_public_keys.jwks",
"example_extension_parameter": "example_value"
}

3.2.2. Client Registration Error Response

When an OAuth 2.0 error condition occurs, such as the client
presenting an invalid initial access token, the authorization server
returns an error response appropriate to the OAuth 2.0 token type.

When a registration error condition occurs, the authorization server
returns an HTTP 400 status code (unless otherwise specified) with
content type "application/json" consisting of a JSON object [RFC7159]
describing the error in the response body.

Two members are defined for inclusion in the JSON object:

error
REQUIRED. Single ASCII error code string.

error_description
OPTIONAL. Human-readable ASCII text description of the error used
for debugging.

Other members MAY also be included and, if they are not understood,
they MUST be ignored.

This specification defines the following error codes:

invalid_redirect_uri
The value of one or more redirection URIs is invalid.

invalid_client_metadata
The value of one of the client metadata fields is invalid and the
server has rejected this request. Note that an authorization
server MAY choose to substitute a valid value for any requested
parameter of a client's metadata.

invalid_software_statement
The software statement presented is invalid.

unapproved_software_statement
The software statement presented is not approved for use by this
authorization server.

The following is a non-normative example of an error response
resulting from a redirection URI that has been blacklisted by the
authorization server (with line wraps breaks within values for display
purposes only):

HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache

{
"error": "invalid_redirect_uri",
"error_description": "The redirection URI
http://sketchy.example.com is not allowed by this server."
}
Following

The following is a non-normative example of an error response
resulting from an inconsistent combination of "response_types" and
"grant_types" values (with line wraps breaks within values for display
purposes only):

HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache

{
"error": "invalid_client_metadata",
"error_description": "The grant type 'authorization_code' must be
registered along with the response type 'code' but found only
'implicit' instead."
}

4. IANA Considerations

4.1. OAuth Dynamic Client Registration Metadata Registry

This specification establishes the OAuth "OAuth Dynamic Client Registration
Metadata Registry.
Metadata" registry.

OAuth registration client metadata names and descriptions are
registered with a Specification Required ([RFC5226]) after a two-week
review period on the oauth-ext-review@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of names prior to publication, the Designated Experts may
approve registration once they are satisfied that such a
specification will be published, per [RFC7120].

Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register OAuth Dynamic
Client Registration Metadata name: example").

Within the review period, the Designated Experts will either approve
or deny the registration request, communicating this decision to the
review list and IANA. Denials should include an explanation and, if
applicable, suggestions as to how to make the request successful.

IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.

4.1.1. Registration Template

Client Metadata Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case-
insensitive manner SHOULD NOT be accepted.

Client Metadata Description:
Brief description of the metadata value (e.g., "Example
description").

Change Controller:
For Standards Track RFCs, list "IESG". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.

Specification Document(s):
Reference to the document or documents that specify the token
endpoint authorization method, client
metadata definition, preferably including a URI that can be used
to retrieve a copy of the documents. An indication of the
relevant sections may also be included but is not required.

4.1.2. Initial Registry Contents

The initial contents of the OAuth "OAuth Dynamic Client Registration
Metadata Registry
Metadata" registry are:

o Client Metadata Name: "redirect_uris"
o Client Metadata Description: Array of redirection URIs for use in
redirect-based flows
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591
o Client Metadata Name: "token_endpoint_auth_method"
o Client Metadata Description: Requested authentication method for
the token endpoint
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "grant_types"
o Client Metadata Description: Array of OAuth 2.0 grant types that
the client may use
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "response_types"
o Client Metadata Description: Array of the OAuth 2.0 response types
that the client may use
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "client_name"
o Client Metadata Description: Human-readable name of the client to
be presented to the user
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "client_uri"
o Client Metadata Description: URL of a web page providing
information about the client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "logo_uri"
o Client Metadata Description: URL that references a logo for the
client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "scope"
o Client Metadata Description: Space-separated list of OAuth 2.0
scope values
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591
o Client Metadata Name: "contacts"
o Client Metadata Description: Array of strings representing ways to
contact people responsible for this client, typically email
addresses
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "tos_uri"
o Client Metadata Description: URL that points to a human-readable
terms of service document for the client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "policy_uri"
o Client Metadata Description: URL that points to a human-readable
policy document for the client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "jwks_uri"
o Client Metadata Description: URL referencing the client's JSON Web
Key Set [RFC7517] document representing the client's public keys
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "jwks"
o Client Metadata Description: Client's JSON Web Key Set [RFC7517]
document representing the client's public keys
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "software_id"
o Client Metadata Description: Identifier for the software that
comprises a client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "software_version"
o Client Metadata Description: Version identifier for the software
that comprises a client
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "client_id"
o Client Metadata Description: Client identifier
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591
o Client Metadata Name: "client_secret"
o Client Metadata Description: Client secret
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "client_id_issued_at"
o Client Metadata Description: Time at which the client identifier
was issued
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Client Metadata Name: "client_secret_expires_at"
o Client Metadata Description: Time at which the client secret will
expire
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

4.2. OAuth Token Endpoint Authentication Methods Registry

This specification establishes the OAuth "OAuth Token Endpoint
Authentication Methods Registry. Methods" registry.

Additional values for use as "token_endpoint_auth_method" values are
registered with a Specification Required ([RFC5226]) after a two-week
review period on the oauth-ext-review@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Experts may
approve registration once they are satisfied that such a
specification will be published, per [RFC7120].

Registration requests must be sent to the oauth-ext-review@ietf.org
mailing list for review and comment, with an appropriate subject
(e.g., "Request to register token_endpoint_auth_method value:
example").

IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.

4.2.1. Registration Template

Token Endpoint Authorization Authentication Method Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case-
insensitive manner SHOULD NOT be accepted.

Change Controller:
For Standards Track RFCs, list "IESG". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.

Specification Document(s):
Reference to the document or documents that specify the token
endpoint authorization authentication method, preferably including a URI that
can be used to retrieve a copy of the document or documents. An
indication of the relevant sections may also be included but is
not required.

4.2.2. Initial Registry Contents

The initial contents of the OAuth "OAuth Token Endpoint Authentication
Methods Registry
Methods" registry are:

o Token Endpoint Authorization Authentication Method Name: "none"
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Token Endpoint Authorization Authentication Method Name: "client_secret_post"
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

o Token Endpoint Authorization Authentication Method Name: "client_secret_basic"
o Change Controller: IESG
o Specification Document(s): this document (RFC 7591) RFC 7591

5. Security Considerations

Since requests to the client registration endpoint result in the
transmission of clear-text credentials (in the HTTP request and
response), the authorization server MUST require the use of a
Transport Layer Security (TLS)
transport-layer security mechanism when sending requests to the
registration endpoint. The server MUST support TLS 1.2 [RFC5246] and
MAY support additional TLS transport-layer security mechanisms meeting
its security requirements. When using TLS, the client MUST perform a
TLS/SSL server certificate check, per RFC 6125 [RFC6125].
Implementation security considerations can be found in
Recommendations for Secure Use of TLS and DTLS [RFC7525]. [BCP195].

For clients that use redirect-based grant types such as
"authorization_code" and "implicit", authorization servers MUST
require clients to register their redirection URI values. This can
help mitigate attacks where rogue actors inject and impersonate a
validly registered client and intercept its authorization code or
tokens through an invalid redirection URI or open redirector.
Additionally, in order to prevent hijacking of the return values of
the redirection, registered redirection URI values MUST be one of:

o A remote web site protected by TLS
(e.g., https://client.example.com/oauth_redirect)
o A web site hosted on the local machine using an HTTP URI
(e.g., http://localhost:8080/oauth_redirect)
o A non-HTTP application-specific URL that is available only to the
client application
(e.g., exampleapp://oauth_redirect)

Public clients MAY register with an authorization server using this
protocol, if the authorization server's policy allows them. Public
clients use a "none" value for the "token_endpoint_auth_method"
metadata field and are generally used with the "implicit" grant type.
Often these clients will be short-lived in-browser applications
requesting access to a user's resources and access is tied to a
user's active session at the authorization server. Since such
clients often do not have long-term storage, it is possible that such
clients would need to re-register every time the browser application
is loaded. To avoid the resulting proliferation of dead client
identifiers, an authorization server MAY decide to expire
registrations for existing clients meeting certain criteria after a
period of time has elapsed. Alternatively, such clients could be
registered on the server where the in-browser application's code is
served from, and the client's configuration could be pushed to the
browser alongside the code.

Since different OAuth 2.0 grant types have different security and
usage parameters, properties, an authorization server MAY require separate
registrations for a piece of software to support multiple grant
types. For instance, an authorization server might require that all
clients using the "authorization_code" grant type make use of a
client secret for the "token_endpoint_auth_method" but any clients
using the "implicit" grant type not use any authentication at the
token endpoint. In such a situation, a server MAY disallow clients
from registering for both the "authorization_code" and "implicit"
grant types simultaneously. Similarly, the "authorization_code"
grant type is used to represent access on behalf of an end-user, but
the "client_credentials" grant type represents access on behalf of
the client itself. For security reasons, an authorization server
could require that different scopes be used for these different use
cases, and, as a consequence, it MAY disallow these two grant types
from being registered together by the same client. In all of these
cases, the authorization server would respond with an
"invalid_client_metadata" error response.

Unless used as a claim in a software statement, the authorization
server MUST treat all client metadata as self-asserted. For
instance, a rogue client might use the name and logo of a legitimate
client that it is trying to impersonate. Additionally, a rogue
client might try to use the software identifier or software version
of a legitimate client to attempt to associate itself on the
authorization server with instances of the legitimate client. To
counteract this, an authorization server MUST take appropriate steps
to mitigate this risk by looking at the entire registration request
and client configuration. For instance, an authorization server
could issue a warning if the domain/site of the logo doesn't match
the domain/site of redirection URIs. An authorization server could
also refuse registration requests from a known software identifier
that is requesting different redirection URIs or a different client
URI. An authorization server can also present warning messages to
end-users about dynamically registered clients in all cases,
especially if such clients have been recently registered or have not
been trusted by any users at the authorization server before.

In a situation where the authorization server is supporting open
client registration, it must be extremely careful with any URL
provided by the client that will be displayed to the user (e.g.,
"logo_uri", "tos_uri", "client_uri", and "policy_uri"). For
instance, a rogue client could specify a registration request with a
reference to a drive-by download in the "policy_uri", enticing the
user to click on it during the authorization. The authorization
server SHOULD check to see if the "logo_uri", "tos_uri",
"client_uri", and "policy_uri" have the same host and scheme as the
those defined in the array of "redirect_uris" and that all of these
URIs resolve to valid web pages. Since these URI values that are
intended to be displayed to the user at the authorization page, the
authorization server SHOULD protect the user from malicious content
hosted at the URLs where possible. For instance, before presenting
the URLs to the user at the authorization page, the authorization
server could download the content hosted at the URLs, check the
content against a malware scanner and blacklist filter, determine
whether or not there is mixed secure and non-secure content at the
URL, and other possible server-side mitigations. Note that the
content in these URLs can change at any time and the authorization
server cannot provide complete confidence in the safety of the URLs,
but these practices could help. To further mitigate this kind of
threat, the authorization server can also warn the user that the URL
links have been provided by a third party, should be treated with
caution, and are not hosted by the authorization server itself. For
instance, instead of providing the links directly in an HTML anchor,
the authorization server can direct the user to an interstitial
warning page before allowing the user to continue to the target URL.

Clients MAY use both the direct JSON object and the JWT-encoded
software statement to present client metadata to the authorization
server as part of the registration request. A software statement is
cryptographically protected and represents claims made by the issuer
of the statement, while the JSON object represents the self-asserted
claims made by the client or developer directly. If the software
statement is valid and signed by an acceptable authority (such as the
software API publisher), the values of client metadata within the
software statement MUST take precedence over those metadata values
presented in the plain JSON object, which could have been intercepted
and modified.

Like all metadata values, the software statement is an item that is
self-asserted by the client, even though its contents have been
digitally signed or MACed by the issuer of the software statement.
As such, presentation of the software statement is not sufficient in
most cases to fully identify a piece of client software. An initial
access token, in contrast, does not necessarily contain information
about a particular piece of client software but instead represents
authorization to use the registration endpoint. An authorization
server MUST consider the full registration request, including the
software statement, initial access token, and JSON client metadata
values, when deciding whether to honor a given registration request.

If an authorization server receives a registration request for a
client that is not intended to have multiple instances registered
simultaneously and the authorization server can infer a duplication
of registration (e.g., it uses the same "software_id" and
"software_version" values as another existing client), the server
SHOULD treat the new registration as being suspect and reject the
registration. It is possible that the new client is trying to
impersonate the existing client in order to trick users into
authorizing it, or that the original registration is no longer valid.
The details of managing this situation are specific to the
authorization server deployment and outside the scope of this
specification.

Since a client identifier is a public value that can be used to
impersonate a client at the authorization endpoint, an authorization
server that decides to issue the same client identifier to multiple
instances of a registered client needs to be very particular about
the circumstances under which this occurs. For instance, the
authorization server can limit a given client identifier to clients
using the same redirect-based flow and the same redirection URIs. An
authorization server SHOULD NOT issue the same client secret to
multiple instances of a registered client, even if they are issued
the same client identifier, or else the client secret could be
leaked, allowing malicious impostors to impersonate a confidential
client.

6. Privacy Considerations

As the protocol described in this specification deals almost
exclusively with information about software and not people, there are
very few privacy concerns for its use. The notable exception is the
"contacts" field as defined in Client Metadata (Section 2), Section 2, which contains contact
information for the developers or other parties responsible for the
client software. These values are intended to be displayed to end-users end-
users and will be available to the administrators of the
authorization server. As such, the developer may wish to provide an
email address or other contact information expressly dedicated to the
purpose of supporting the client instead of using their personal or
professional addresses. Alternatively, the developer may wish to
provide a collective email address for the client to allow for
continuing contact and support of the client software after the
developer moves on and someone else takes over that responsibility.

In general, the metadata for a client, such as the client name and
software identifier, are common across all instances of a piece of
client software and therefore pose no privacy issues for end-users.
Client identifiers, on the other hand, are often unique to a specific
instance of a client. For clients such as web sites that are used by
many users, there may not be significant privacy concerns regarding
the client identifier, but for clients such as native applications
that are installed on a single end-user's device, the client
identifier could be uniquely tracked during OAuth 2.0 transactions
and its use tied to that single end-user. However, as the client
software still needs to be authorized by a resource owner through an
OAuth 2.0 authorization grant, this type of tracking can occur
whether or not the client identifier is unique by correlating the
authenticated resource owner with the requesting client identifier.

Note that clients are forbidden by this specification from creating
their own client identifier. If the client were able to do so, an
individual client instance could be tracked across multiple colluding
authorization servers, leading to privacy and security issues.
Additionally, client identifiers are generally issued uniquely per
registration request, even for the same instance of software. In
this way, an application could marginally improve privacy by
registering multiple times and appearing to be completely separate
applications. However, this technique does incur significant
usability cost in the form of requiring multiple authorizations per
resource owner and is therefore unlikely to be used in practice.

7. References

7.1. Normative References

[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/bcp195>.

[IANA.Language]
IANA, "Language Subtag Registry",
<http://www.iana.org/assignments/
language-subtag-registry>.
<http://www.iana.org/assignments/language-subtag-
registry>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/
RFC2119, 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/
RFC5246, 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.

[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <http://www.rfc-editor.org/info/rfc5646>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>.

[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.

[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/
RFC6750, 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>.

[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <http://www.rfc-editor.org/info/rfc7120>.

[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.

[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <http://www.rfc-editor.org/info/rfc7515>.

[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/
RFC7517, 10.17487/RFC7517, May 2015,
<http://www.rfc-editor.org/info/rfc7517>.

[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>.

[RFC7522] Campbell, B., Mortimore, C., and M. Jones, "Security
Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
Client Authentication and Authorization Grants", RFC 7522,
DOI 10.17487/RFC7522, May 2015,
<http://www.rfc-editor.org/info/rfc7522>.

[RFC7523] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
(JWT) Profile for OAuth 2.0 Client Authentication and
Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
2015, <http://www.rfc-editor.org/info/rfc7523>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>.

7.2. Informative References

[OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0", November 2014,
<http://openid.net/specs/
openid-connect-registration-1_0.html>.
openid-connect-discovery-1_0.html>.

[OpenID.Registration]
Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect
Dynamic Client Registration 1.0", November 2014,
<http://openid.net/specs/
openid-connect-registration-1_0.html>.

[RFC7592] Richer, J., Jones, M., Bradley, J., and M. Machulak,
"OAuth 2.0 Dynamic Client Registration Management
Protocol", RFC 7592, DOI 10.17487/RFC7592, June July 2015,
<http://www.rfc-editor.org/info/rfc7592>.

[UMA-Core]
Hardjono, T., Maler, E., Machulak, M., and D. Catalano,
"User-Managed Access (UMA) Profile of OAuth 2.0", Work in
Progress, draft-hardjono-oauth-umacore-13, April 2015.

Appendix A. Use Cases

This appendix describes different ways that this specification can be
utilized, including describing some of the choices that may need to
be made. Some of the choices are independent and can be used in
combination, whereas some of the choices are interrelated.

A.1. Open versus Protected Dynamic Client Registration

A.1.1. Open Dynamic Client Registration

Authorization servers that support open registration allow
registrations to be made with no initial access token. This allows
all client software to register with the authorization server.

A.1.2. Protected Dynamic Client Registration

Authorization servers that support protected registration require
that an initial access token be used when making registration
requests. While the method by which a client or developer receives
this initial access token and the method by which the authorization
server validates this initial access token are out of scope for this
specification, a common approach is for the developer to use a manual
preregistration portal at the authorization server that issues an
initial access token to the developer.

A.2. Registration without or with Software Statements

A.2.1. Registration without a Software Statement

When a software statement is not used in the registration request,
the authorization server must be willing to use client metadata
values without them being digitally signed or MACed (and thereby
attested to) by any authority. (Note that this choice is independent
of the Open versus Protected choice, and that an initial access token
is another possible form of attestation.)

A.2.2. Registration with a Software Statement

A software statement can be used in a registration request to provide
attestation by an authority for a set of client metadata values.
This can be useful when the authorization server wants to restrict
registration to client software attested to by a set of authorities
or when it wants to know that multiple registration requests refer to
the same piece of client software.

A.3. Registration by the Client or Developer

A.3.1. Registration by the Client

In some use cases, client software will dynamically register itself
with an authorization server to obtain a client identifier and other
information needed to interact with the authorization server. In
this case, no client identifier for the authorization server is
packaged with the client software.

A.3.2. Registration by the Developer

In some cases, the developer (or development software being used by
the developer) will preregister the client software with the
authorization server or a set of authorization servers. In this
case, the client identifier value(s) for the authorization server(s)
can be packaged with the client software.

A.4. Client ID per Client Instance or per Client Software

A.4.1. Client ID per Client Software Instance

In some cases, each deployed instance of a piece of client software
will dynamically register and obtain distinct client identifier
values. This can be advantageous, for instance, if the code flow is
being used, as it also enables each client instance to have its own
client secret. This can be useful for native clients, which cannot
maintain the secrecy of a client secret value packaged with the
software, but which may be able to maintain the secrecy of a per-
instance client secret.

A.4.2. Client ID Shared among All Instances of Client Software

In some cases, each deployed instance of a piece of client software
will share a common client identifier value. For instance, this is
often the case for in-browser clients using the implicit flow, when
no client secret is involved. Particular authorization servers might
choose, for instance, to maintain a mapping between software
statement values and client identifier values, and return the same
client identifier value for all registration requests for a
particular piece of software. The circumstances under which an
authorization server would do so, and the specific software statement
characteristics required in this case, are beyond the scope of this
specification.

A.5. Stateful or Stateless Registration

A.5.1. Stateful Client Registration

In some cases, authorization servers will maintain state about
registered clients, typically indexing this state using the client
identifier value. This state would typically include the client
metadata values associated with the client registration, and possibly
other state specific to the authorization server's implementation.
When stateful registration is used, operations to support retrieving
and/or updating this state may be supported. One possible set of
operations upon stateful registrations is described in [RFC7592].

A.5.2. Stateless Client Registration

In some cases, authorization servers will be implemented in a manner
the enables them to not maintain any local state about registered
clients. One means of doing this is to encode all the registration
state in the returned client identifier value, and possibly
encrypting the state to the authorization server to maintain the
confidentiality and integrity of the state.

Acknowledgments

The authors thank the OAuth Working Group, the User-Managed Access
Working Group, and the OpenID Connect Working Group participants for
their input to this document. In particular, the following
individuals have been instrumental in their review and contribution
to various draft versions of this document: Amanda Anganes, Derek
Atkins, Tim Bray, Domenico Catalano, Donald Coffin, Vladimir
Dzhuvinov, George Fletcher, Thomas Hardjono, Phil Hunt, William Kim, Torsten
Lodderstedt, Eve Maler, Josh Mandel, Nov Matake, Tony Nadalin, Nat
Sakimura, Christian Scholz, and Hannes Tschofenig.

Authors' Addresses

Justin Richer (editor)

EMail:

Email: ietf@justin.richer.org

Michael B. Jones
Microsoft

EMail:

Email: mbj@microsoft.com
URI: http://self-issued.info/

John Bradley
Ping Identity

EMail:

Email: ve7jtb@ve7jtb.com

Maciej Machulak
Newcastle University

EMail:

Email: maciej.machulak@gmail.com

Phil Hunt
Oracle Corporation

EMail:

Email: phil.hunt@yahoo.com