rfc9444.original   rfc9444.txt 
ACME Working Group O. Friel Internet Engineering Task Force (IETF) O. Friel
Internet-Draft R. Barnes Request for Comments: 9444 R. Barnes
Intended status: Standards Track Cisco Category: Standards Track Cisco
Expires: 2 September 2023 T. Hollebeek ISSN: 2070-1721 T. Hollebeek
DigiCert DigiCert
M. Richardson M. Richardson
Sandelman Software Works Sandelman Software Works
1 March 2023 August 2023
Automated Certificate Management Environment (ACME) for Subdomains Automated Certificate Management Environment (ACME) for Subdomains
draft-ietf-acme-subdomains-07
Abstract Abstract
This document specifies how Automated Certificate Management This document specifies how Automated Certificate Management
Environment (ACME) can be used by a client to obtain a certificate Environment (ACME) can be used by a client to obtain a certificate
for a subdomain identifier from a certification authority. This for a subdomain identifier from a certification authority.
document specifies how a client can fulfill a challenge against an Additionally, this document specifies how a client can fulfill a
ancestor domain but may not need to fulfill a challenge against the challenge against an ancestor domain but may not need to fulfill a
explicit subdomain if certification authority policy allows issuance challenge against the explicit subdomain if certification authority
of the subdomain certificate without explicit subdomain ownership policy allows issuance of the subdomain certificate without explicit
proof. subdomain ownership proof.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79.
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and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9444.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology
3. ACME Workflow and Identifier Requirements . . . . . . . . . . 5 3. ACME Workflow and Identifier Requirements
4. ACME Issuance of Subdomain Certificates . . . . . . . . . . . 6 4. ACME Issuance of Subdomain Certificates
4.1. Authorization Object . . . . . . . . . . . . . . . . . . 7 4.1. Authorization Object
4.2. Pre-Authorization . . . . . . . . . . . . . . . . . . . . 8 4.2. Pre-authorization
4.3. New Orders . . . . . . . . . . . . . . . . . . . . . . . 9 4.3. New Orders
4.4. Directory Object Metadata . . . . . . . . . . . . . . . . 11 4.4. Directory Object Metadata
5. Illustrative Call Flow . . . . . . . . . . . . . . . . . . . 11 5. Illustrative Call Flow
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations
6.1. Authorization Object Fields Registry . . . . . . . . . . 17 6.1. Authorization Object Fields Registry
6.2. Directory Object Metadata Fields Registry . . . . . . . . 17 6.2. Directory Object Metadata Fields Registry
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 7. Security Considerations
7.1. Client Account Security . . . . . . . . . . . . . . . . . 19 7.1. Client Account Security
7.2. Subdomain Determination . . . . . . . . . . . . . . . . . 19 7.2. Subdomain Determination
7.3. ACME Server Policy Considerations . . . . . . . . . . . . 19 7.3. ACME Server Policy Considerations
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 8. References
8.1. Normative References . . . . . . . . . . . . . . . . . . 20 8.1. Normative References
8.2. Informative References . . . . . . . . . . . . . . . . . 21 8.2. Informative References
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses
1. Introduction 1. Introduction
ACME [RFC8555] defines a protocol that a certification authority (CA) ACME [RFC8555] defines a protocol that a certification authority (CA)
and an applicant can use to automate the process of domain name and an applicant can use to automate the process of domain name
ownership validation and X.509v3 (PKIX) [RFC5280] certificate ownership validation and X.509v3 (PKIX) [RFC5280] certificate
issuance. The CA is the ACME server and the applicant is the ACME issuance. The CA is the ACME server and the applicant is the ACME
client, and the client uses the ACME protocol to request certificate client, and the client uses the ACME protocol to request certificate
issuance from the server. This document outlines how ACME can be issuance from the server. This document outlines how ACME can be
used to issue subdomain certificates, without requiring the ACME used to issue subdomain certificates without requiring the ACME
client to explicitly fulfill an ownership challenge against the client to explicitly fulfill an ownership challenge against the
subdomain identifiers - the ACME client need only fulfill an subdomain identifiers -- the ACME client need only fulfill an
ownership challenge against an ancestor domain identifier. ownership challenge against an ancestor domain identifier.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
The following terms are defined in DNS Terminology [RFC8499] and are The following terms are defined in "DNS Terminology" [RFC8499] and
reproduced here: are reproduced here:
* Label: An ordered list of zero or more octets that makes up a Label:
portion of a domain name. Using graph theory, a label identifies An ordered list of zero or more octets that makes up a portion of
one node in a portion of the graph of all possible domain names. a domain name. Using graph theory, a label identifies one node in
a portion of the graph of all possible domain names.
* Domain Name: An ordered list of one or more labels. Domain Name:
An ordered list of one or more labels.
* Fully-Qualified Domain Name (FQDN): This is often just a clear way Fully-Qualified Domain Name (FQDN):
of saying the same thing as "domain name of a node", as outlined This is often just a clear way of saying the same thing as "domain
above. However, the term is ambiguous. Strictly speaking, a name of a node", as outlined above. However, the term is
fully-qualified domain name would include every label, including ambiguous. Strictly speaking, a fully-qualified domain name would
the zero-length label of the root: such a name would be written include every label, including the zero-length label of the root:
"www.example.net." (note the terminating dot). But, because every such a name would be written www.example.net. (note the
name eventually shares the common root, names are often written terminating dot). But, because every name eventually shares the
relative to the root (such as "www.example.net") and are still common root, names are often written relative to the root (such as
called "fully qualified". This term first appeared in [RFC0819]. www.example.net) and are still called "fully qualified". This
In this document, names are often written relative to the root. term first appeared in [RFC0819]. In this document, names are
often written relative to the root.
The following definition for "subdomain" is taken from DNS The following definition for "subdomain" is taken from "DNS
Terminology [RFC8499] and reproduced here, however the definition is Terminology" [RFC8499] and reproduced here; however, the definition
ambiguous and is further clarified below: is ambiguous and is further clarified below:
* Subdomain: "A domain is a subdomain of another domain if it is Subdomain:
contained within that domain. This relationship can be tested by "A domain is a subdomain of another domain if it is contained
seeing if the subdomain's name ends with the containing domain's within that domain. This relationship can be tested by seeing if
name." (Quoted from Section 3.1 of [RFC1034].) For example, in the subdomain's name ends with the containing domain's name."
the host name "nnn.mmm.example.com", both "mmm.example.com" and (Quoted from Section 3.1 of [RFC1034].) For example, in the host
"nnn.mmm.example.com" are subdomains of "example.com". Note that name nnn.mmm.example.com, both mmm.example.com and
the comparisons here are done on whole labels; that is, nnn.mmm.example.com are subdomains of example.com. Note that the
"ooo.example.com" is not a subdomain of "oo.example.com". comparisons here are done on whole labels; that is,
ooo.example.com is not a subdomain of oo.example.com.
The definition is ambiguous as it appears to allow a subdomain to The definition is ambiguous as it appears to allow a subdomain to
include the given domain. That is, "mmm.example.com" ends with include the given domain. That is, mmm.example.com ends with
"mmm.example.com" and thus is a subdomain of itself. This document mmm.example.com and thus is a subdomain of itself. This document
interprets the first sentence of the above definition as meaning "A interprets the first sentence of the above definition as meaning "a
domain is a subdomain of a different domain if it is contained within domain is a subdomain of a different domain if it is contained within
that different domain.". A domain cannot be a subdomain of itself. that different domain". A domain cannot be a subdomain of itself.
For example, "mmm.example.com" is not a subdomain of For example, mmm.example.com is not a subdomain of mmm.example.com.
"mmm.example.com".
The following additional terms are used in this document: The following additional terms are used in this document:
* Certification Authority (CA): An organization that is responsible Certification Authority (CA):
for the creation, issuance, revocation, and management of An organization that is responsible for the creation, issuance,
Certificates. The term applies equally to both Root CAs and revocation, and management of Certificates. The term applies
Subordinate CAs. Refer to [RFC5280] for detailed information on equally to both root CAs and subordinate CAs. Refer to [RFC5280]
Certification Authorities. for detailed information on Certification Authorities.
* CSR: Certificate Signing Request as defined in [RFC2986] CSR:
Certificate Signing Request, as defined in [RFC2986].
* Ancestor Domain: a domain is an ancestor domain of a subdomain if Ancestor Domain:
it contains that subdomain and has less labels than that A domain is an ancestor domain of a subdomain if it contains that
subdomain. A domain cannot be an ancestor domain of itself. For subdomain and has less labels than that subdomain. A domain
example, for the host name "nnn.mmm.example.com", both cannot be an ancestor domain of itself. For example, for the host
"mmm.example.com" and "example.com" are ancestor domains of name nnn.mmm.example.com, both mmm.example.com and example.com are
"nnn.mmm.example.com". However, "nnn.mmm.example.com" is not an ancestor domains of nnn.mmm.example.com. However,
ancestor domain of "nnn.mmm.example.com". Note that the nnn.mmm.example.com is not an ancestor domain of
comparisons here are done on whole labels; that is, nnn.mmm.example.com. Note that the comparisons here are done on
"oo.example.com" is not an ancestor domain of "ooo.example.com". whole labels; that is, oo.example.com is not an ancestor domain of
ooo.example.com.
ACME [RFC8555] defines the following object types which are used in [RFC8555] defines the following object types that are used in this
this document: document:
* Order Object: An ACME order object represents a client's request Order Object: An ACME order object represents a client's request for
for a certificate and is used to track the progress of that order a certificate and is used to track the progress of that order
through to issuance. through to issuance.
* Authorization Object: An ACME authorization object represents a Authorization Object: An ACME authorization object represents a
server's authorization for an account to represent an identifier. server's authorization for an account to represent an identifier.
* Challenge Object: An ACME challenge object represents a server's Challenge Object: An ACME challenge object represents a server's
offer to validate a client's possession of an identifier in a offer to validate a client's possession of an identifier in a
specific way. specific way.
ACME [RFC8555] Section 6.3 introduces the following term which is ACME [RFC8555], Section 6.3 introduces the following term which is
used in this document: used in this document:
* POST-as-GET Request: When a client wishes to fetch a resource from POST-as-GET Request:
the server, then it MUST send a POST request with a signed JWS When a client wishes to fetch a resource from the server, then it
body, where the JWS body is specified in ACME [RFC8555] MUST send a POST request with a signed JSON Web Signature (JWS)
body, where the JWS body is specified in ACME [RFC8555],
Section 6.2. ACME refers to these as "POST-as-GET" requests. Section 6.2. ACME refers to these as "POST-as-GET" requests.
3. ACME Workflow and Identifier Requirements 3. ACME Workflow and Identifier Requirements
A typical ACME [RFC8555] workflow for issuance of certificates is as A typical ACME workflow for issuance of certificates is as follows:
follows:
1. client POSTs a newOrder request that contains a set of 1. Client POSTs a newOrder request that contains a set of identifier
"identifiers" objects in the identifiers field of the ACME order object.
2. server replies with an order object that contains a set of links 2. Server replies with an order object that contains a set of links
to authorization object(s) and a "finalize" URI to authorization object(s) and a finalize URI.
3. client sends POST-as-GET requests to retrieve the authorization 3. Client sends POST-as-GET requests to retrieve the authorization
object(s), with the downloaded authorization object(s) containing object(s), with the downloaded authorization object(s) containing
the "identifier" that the client must prove that they control, the identifier that the client must prove that they control, and
and a set of links to associated challenges objects, one of which a set of links to associated challenges objects, one of which the
the client must fulfill client must fulfill.
4. client proves control over the "identifier" in the authorization 4. Client proves control over the identifier in the authorization
object by completing one of the specified challenges, for object by completing one of the specified challenges, for
example, by publishing a DNS TXT record example, by publishing a DNS TXT record.
5. client POSTs a CSR to the "finalize" API 5. Client POSTs a CSR to the finalize API.
6. server replies with an updated order object that includes a 6. Server replies with an updated order object that includes a
"certificate" URI certificate URI.
7. client sends POST-as-GET request to the "certificate" URI to 7. Client sends a POST-as-GET request to the certificate URI to
download the certificate download the certificate.
ACME places the following restrictions on "identifiers": ACME places the following restrictions on identifiers:
* [RFC8555], Section 7.1.3: The authorizations required are dictated * [RFC8555], Section 7.1.3: "The authorizations required are
by server policy; there may not be a 1:1 relationship between the dictated by server policy; there may not be a 1:1 relationship
order identifiers and the authorizations required. between the order identifiers and the authorizations required."
* [RFC8555], Section 7.1.4: the only type of "identifier" defined by * [RFC8555], Section 7.1.4: The only type of identifier defined by
the ACME specification is an FQDN: "The only type of identifier the ACME specification is an FQDN: "The only type of identifier
defined by this specification is a fully qualified domain name defined by this specification is a fully qualified domain name
(type: "dns"). The domain name MUST be encoded in the form in (type: "dns"). The domain name MUST be encoded in the form in
which it would appear in a certificate." which it would appear in a certificate."
* [RFC8555], Section 7.4: the "identifier" in the CSR request must * [RFC8555], Section 7.4: The identifier in the CSR request must
match the "identifier" in the newOrder request: "The CSR MUST match the identifier in the newOrder request: "The CSR MUST
indicate the exact same set of requested identifiers as the indicate the exact same set of requested identifiers as the
initial newOrder request." initial newOrder request."
* [RFC8555], Section 8.3: the "identifier", or FQDN, in the * [RFC8555], Section 8.3: The identifier, or FQDN, in the
authorization object must be used when fulfilling challenges via authorization object must be used when fulfilling challenges via
HTTP: "Construct a URL by populating the URL template ... where HTTP: "Construct a URL by populating the URL template ... where
the domain field is set to the domain name being verified" the domain field is set to the domain name being verified."
* [RFC8555], Section 8.4: the "identifier", or FQDN, in the * [RFC8555], Section 8.4: The identifier, or FQDN, in the
authorization object must be used when fulfilling challenges via authorization object must be used when fulfilling challenges via
DNS: "The client constructs the validation domain name by DNS: "The client constructs the validation domain name by
prepending the label "_acme-challenge" to the domain name being prepending the label "_acme-challenge" to the domain name being
validated." validated."
ACME does not mandate that the "identifier" in a newOrder request ACME does not mandate that the identifier in a newOrder request
matches the "identifier" in authorization objects. matches the identifier in authorization objects.
The base ACME [RFC8555] document only specifies the "dns" identifier The ACME base document [RFC8555] only specifies the "dns" identifier
type. Additional identifiers may be defined and registered in the type. Additional identifiers may be defined and registered in the
IANA [ACME-Identifier-Types] registry. For example, [RFC8738] IANA [ACME-Identifier-Types] registry. For example, [RFC8738]
specifies the "ip" identifier type. This document is only relevant specifies the "ip" identifier type. This document is only relevant
for the "dns" identifier type. for the "dns" identifier type.
Note also that ACME supports multiple different validation methods Note that ACME supports multiple different validation methods that
that can be used to fulfill challenges and prove ownership of can be used to fulfill challenges and prove ownership of identifiers.
identifiers. Validation methods are registered in the IANA Validation methods are registered in the IANA
[ACME-Validation-Methods] registry. This document does not mandate [ACME-Validation-Methods] registry. This document does not mandate
use of any particular validation method or methods. ACME server use of any particular validation method or methods. ACME server
policy dictates which validation methods are supported. See policy dictates which validation methods are supported. See
Section 7.3 for more information on ACME server policy. Section 7.3 for more information on ACME server policy.
4. ACME Issuance of Subdomain Certificates 4. ACME Issuance of Subdomain Certificates
As noted in the previous section, ACME [RFC8555] does not mandate As noted in the previous section, ACME [RFC8555] does not mandate
that the "identifier" in a newOrder request matches the "identifier" that the identifier in a newOrder request matches the identifier in
in authorization objects. This means that the ACME specification authorization objects. This means that the ACME specification does
does not preclude an ACME server processing newOrder requests and not preclude an ACME server processing newOrder requests and issuing
issuing certificates for a subdomain without requiring a challenge to certificates for a subdomain without requiring a challenge to be
be fulfilled against that explicit subdomain. fulfilled against that explicit subdomain.
ACME server policy could allow issuance of certificates for a ACME server policy could allow issuance of certificates for a
subdomain to a client where the client only has to fulfill an subdomain to a client where the client only has to fulfill an
authorization challenge for an ancestor domain of that subdomain. authorization challenge for an ancestor domain of that subdomain.
This allows a flow where a client proves ownership of, for example, For example, this allows for a flow where a client proves ownership
"example.org" and then successfully obtains a certificate for of example.org and then successfully obtains a certificate for
"sub.example.org". sub.example.org.
ACME server policy is out of scope of this document, however, some ACME server policy is out of scope of this document; however, some
commentary is provided in Section 7.3. commentary is provided in Section 7.3.
Clients need a mechanism to instruct the ACME server that they are Clients need a mechanism to instruct the ACME server that they are
requesting authorization for all subdomains subordinate to the requesting authorization for all subdomains subordinate to the
specified domain, as opposed to just requesting authorization for an specified domain, as opposed to just requesting authorization for an
explicit domain identifier. Clients need a mechanism to do this in explicit domain identifier. Clients need a mechanism to do this in
both newAuthz and newOrder requests. ACME servers need a mechanism both newAuthz and newOrder requests. ACME servers need a mechanism
to indicate to clients that authorization objects are valid for all to indicate to clients that authorization objects are valid for all
subdomains under the specified domain. These are described in this subdomains under the specified domain. These are described in this
section. section.
4.1. Authorization Object 4.1. Authorization Object
ACME ([RFC8555], Section 7.1.4) defines the authorization object. ACME ([RFC8555], Section 7.1.4) defines the authorization object.
This document defines a new "subdomainAuthAllowed" field for the This document defines a new subdomainAuthAllowed field for the
authorization object. When ACME server policy allows authorization authorization object. When ACME server policy allows authorization
for subdomains subordinate to a domain, the server indicates this by for subdomains subordinate to a domain, the server indicates this by
including the new "subdomainAuthAllowed" field in the authorization including the new subdomainAuthAllowed field in the authorization
object for that domain identifier: object for that domain identifier:
subdomainAuthAllowed (optional, boolean): If present, this field subdomainAuthAllowed (optional, boolean): If present, this field
MUST be true for authorizations where ACME server policy MUST be true for authorizations where ACME server policy allows
allows certificates to be issued for any subdomain subordinate certificates to be issued for any subdomain subordinate to the
to the domain specified in the 'identifier' field of the domain specified in the identifier field of the authorization
authorization object. object.
The following example shows an authorization object for the domain The following example shows an authorization object for the domain
example.org where the authorization covers the subdomains subordinate example.org, where the authorization covers the subdomains
to example.org. subordinate to example.org.
{ {
"status": "valid", "status": "valid",
"expires": "2023-09-01T14:09:07.99Z", "expires": "2023-09-01T14:09:07.99Z",
"identifier": { "identifier": {
"type": "dns", "type": "dns",
"value": "example.org" "value": "example.org"
}, },
"challenges": [ "challenges": [
{ {
"url": "https://example.com/acme/chall/prV_B7yEyA4", "url": "https://example.com/acme/chall/prV_B7yEyA4",
"type": "http-01", "type": "http-01",
"status": "valid", "status": "valid",
"token": "DGyRejmCefe7v4NfDGDKfA", "token": "DGyRejmCefe7v4NfDGDKfA",
"validated": "2014-12-01T12:05:58.16Z" "validated": "2014-12-01T12:05:58.16Z"
} }
], ],
"subdomainAuthAllowed": true "subdomainAuthAllowed": true
} }
If the "subdomainAuthAllowed" field is not included, then the assumed If the subdomainAuthAllowed field is not included, then the assumed
default value is false. default value is false.
If ACME server policy allows issuance of certificates containing If ACME server policy allows issuance of certificates containing
wildcard identifiers under that authorization object, then the server wildcard identifiers under that authorization object, then the server
SHOULD include the "wildcard" field with a value of true, as per SHOULD include the wildcard field with a value of true, as per
[RFC8555], Section 7.1.4. [RFC8555], Section 7.1.4.
4.2. Pre-Authorization 4.2. Pre-authorization
The basic ACME workflow has authorization objects created reactively The basic ACME workflow has authorization objects created reactively
in response to a certificate order. ACME also allows for pre- in response to a certificate order. ACME also allows for pre-
authorization, where clients obtain authorization for an identifier authorization, where clients obtain authorization for an identifier
proactively, outside of the context of a specific issuance. With the proactively, outside of the context of a specific issuance. With the
ACME pre-authorization flow, a client can pre-authorize for a domain ACME pre-authorization flow, a client can pre-authorize for a domain
once, and then issue multiple newOrder requests for certificates with once and then issue multiple newOrder requests for certificates with
identifiers in the subdomains subordinate to that domain. identifiers in the subdomains subordinate to that domain.
ACME [RFC8555], Section 7.4.1 defines the "identifier" object for ACME ([RFC8555], Section 7.4.1) defines the identifier object for
newAuthz requests. This document defines a new newAuthz requests. This document defines a new subdomainAuthAllowed
"subdomainAuthAllowed" field for the "identifier" object: field for the identifier object:
subdomainAuthAllowed (optional, boolean): An ACME client sets subdomainAuthAllowed (optional, boolean): An ACME client sets this
this flag to indicate to the server that it is requesting an flag to indicate to the server that it is requesting an
authorization for the subdomains subordinate to the specified authorization for the subdomains subordinate to the specified
domain identifier value domain identifier value.
Clients include the new "subdomainAuthAllowed" field in the Clients include the new subdomainAuthAllowed field in the identifier
"identifier" object of newAuthz requests to indicate that they are object of newAuthz requests to indicate that they are requesting a
requesting a subdomain authorization. In the following example subdomain authorization. In the following example of a newAuthz
newAuthz payload, the client is requesting pre-authorization for the payload, the client is requesting pre-authorization for the
subdomains subordinate to example.org. subdomains subordinate to example.org.
"payload": base64url({ "payload": base64url({
"identifier": { "identifier": {
"type": "dns", "type": "dns",
"value": "example.org", "value": "example.org",
"subdomainAuthAllowed": true "subdomainAuthAllowed": true
} }
}) })
If the server is willing to allow a single authorization for the If the server is willing to allow a single authorization for the
subdomains, and there is not an existing authorization object for the subdomains and there is not an existing authorization object for the
identifier, then it will create an authorization object and include identifier, then it will create an authorization object and include
the "subdomainAuthAllowed" flag with value of true. the subdomainAuthAllowed flag with a value of true.
If the server policy does not allow creation of subdomain If the server policy does not allow creation of subdomain
authorizations subordinate to that domain, the server can create an authorizations subordinate to that domain, the server can create an
authorization object for the indicated identifier, and MAY include authorization object for the indicated identifier and MAY include the
the "subdomainAuthAllowed" flag with value of false. If the server subdomainAuthAllowed flag with a value of false. If the server
creates an authorization object and does not include the creates an authorization object and does not include the
"subdomainAuthAllowed" flag, then the assumed value is false. subdomainAuthAllowed flag, then the assumed value is false.
In both scenarios, handling of the pre-authorization follows the In both scenarios, handling of the pre-authorization follows the
process documented in ACME [RFC8555], Section 7.4.1. process documented in ACME [RFC8555], Section 7.4.1.
4.3. New Orders 4.3. New Orders
Clients need a mechanism to optionally indicate to servers whether or Clients need a mechanism to optionally indicate to servers whether or
not they are authorized to fulfill challenges against an ancestor not they are authorized to fulfill challenges against an ancestor
domain for a given identifier. For example, if a client places an domain for a given identifier. For example, if a client places an
order for an identifier foo.bar.example.org, and is authorized to order for an identifier foo.bar.example.org and is authorized to
fulfill a challenge against the ancestor domains bar.example.org or fulfill a challenge against the ancestor domains bar.example.org or
example.org, then the client needs a mechanism to indicate control example.org, then the client needs a mechanism to indicate control
over the ancestor domains to the ACME server. over the ancestor domains to the ACME server.
In order to accomplish this, this document defines a new In order to accomplish this, this document defines a new
"ancestorDomain" field for the identifier that is included in order ancestorDomain field for the identifier that is included in order
objects. objects.
ancestorDomain (optional, string): This is an ancestor domain of ancestorDomain (optional, string): This is an ancestor domain of the
the requested identifier. The client MUST be able to fulfill requested identifier. The client MUST be able to fulfill a
a challenge against the ancestor domain. challenge against the ancestor domain.
This field specifies an ancestor domain of the identifier that the This field specifies an ancestor domain of the identifier that the
client has DNS control over, and is capable of fulfilling challenges client has DNS control over and is capable of fulfilling challenges
against. Based on server policy, the server can choose to issue a against. Based on server policy, the server can choose to issue a
challenge against any ancestor domain of the identifier up to and challenge against any ancestor domain of the identifier up to and
including the specified "ancestorDomain", and create a corresponding including the specified ancestorDomain and create a corresponding
authorization object against the chosen identifier. authorization object against the chosen identifier.
In the following example newOrder payload, the client requests a In the following example of a newOrder payload, the client requests a
certificate for identifier foo.bar.example.org and indicates that it certificate for identifier foo.bar.example.org and indicates that it
can fulfill a challenge against the ancestor domain bar.example.org. can fulfill a challenge against the ancestor domain bar.example.org.
The server can then choose to issue a challenge against either The server can then choose to issue a challenge against either
foo.bar.example.org or bar.example.org identifiers. foo.bar.example.org or bar.example.org identifiers.
"payload": base64url({ "payload": base64url({
"identifiers": [ "identifiers": [
{ "type": "dns", { "type": "dns",
"value": "foo.bar.example.org", "value": "foo.bar.example.org",
"ancestorDomain": "bar.example.org" } "ancestorDomain": "bar.example.org" }
], ],
"notBefore": "2023-09-01T00:04:00+04:00", "notBefore": "2023-09-01T00:04:00+04:00",
"notAfter": "2023-09-08T00:04:00+04:00" "notAfter": "2023-09-08T00:04:00+04:00"
}) })
In the following example newOrder payload, the client requests a In the following example of a newOrder payload, the client requests a
certificate for identifier foo.bar.example.org and indicates that it certificate for identifier foo.bar.example.org and indicates that it
can fulfill a challenge against the ancestor domain example.org. The can fulfill a challenge against the ancestor domain example.org. The
server can then choose to issue a challenge against any one of server can then choose to issue a challenge against any one of
foo.bar.example.org, bar.example.org or example.org identifiers. foo.bar.example.org, bar.example.org, or example.org identifiers.
"payload": base64url({ "payload": base64url({
"identifiers": [ "identifiers": [
{ "type": "dns", { "type": "dns",
"value": "foo.bar.example.org", "value": "foo.bar.example.org",
"ancestorDomain": "example.org" } "ancestorDomain": "example.org" }
], ],
"notBefore": "2023-09-01T00:04:00+04:00", "notBefore": "2023-09-01T00:04:00+04:00",
"notAfter": "2023-09-08T00:04:00+04:00" "notAfter": "2023-09-08T00:04:00+04:00"
}) })
If the client is unable to fulfill authorizations against an ancestor If the client is unable to fulfill authorizations against an ancestor
domain, the client should not include the "ancestorDomain" field. domain, the client should not include the ancestorDomain field.
Server newOrder handling generally follows the process documented in Server newOrder handling generally follows the process documented in
ACME, Section 7.4 of [RFC8555]. If the server is willing to allow ACME (Section 7.4 of [RFC8555]). If the server is willing to allow
subdomain authorizations for the domain specified in subdomain authorizations for the domain specified in ancestorDomain,
"ancestorDomain", then it creates an authorization object against then it creates an authorization object against that ancestor domain
that ancestor domain and includes the "subdomainAuthAllowed" flag and includes the subdomainAuthAllowed flag with a value of true.
with a value of true.
If the server policy does not allow creation of subdomain If the server policy does not allow creation of subdomain
authorizations against that ancestor domain, then it can create an authorizations against that ancestor domain, then it can create an
authorization object for the indicated identifier value, and SHOULD authorization object for the indicated identifier value and SHOULD
NOT include the "subdomainAuthAllowed" flag. As the client requested NOT include the subdomainAuthAllowed flag. As the client requested a
a subdomain authorization for the ancestor domain, and not for the subdomain authorization for the ancestor domain and not for the
indicated identifier, there is no need for the server to include the indicated identifier, there is no need for the server to include the
"subdomainAuthAllowed" flag in the authorization object for the subdomainAuthAllowed flag in the authorization object for the
indicated identifier. indicated identifier.
4.4. Directory Object Metadata 4.4. Directory Object Metadata
This document defines a new "subdomainAuthAllowed" ACME directory This document defines a new subdomainAuthAllowed ACME directory
metadata field. An ACME server can advertise support for metadata field. An ACME server can advertise support for
authorization of subdomains by including the "subdomainAuthAllowed" authorization of subdomains by including the subdomainAuthAllowed
boolean flag in its "ACME Directory Metadata Fields" registry: boolean flag in its "ACME Directory Metadata Fields" registry:
subdomainAuthAllowed (optional, bool): Indicates if an ACME subdomainAuthAllowed (optional, bool): Indicates if an ACME server
server supports authorization of subdomains. supports authorization of subdomains.
If not specified, then the assumed default value is false. If an If not specified, then the assumed default value is false. If an
ACME server supports authorization of subdomains, it can indicate ACME server supports authorization of subdomains, it can indicate
this by including this field with a value of "true". this by including this field with a value of "true".
5. Illustrative Call Flow 5. Illustrative Call Flow
The call flow illustrated here uses the ACME pre-authorization flow The call flow illustrated here uses the ACME pre-authorization flow
using DNS-based proof of ownership. using DNS-based proof of ownership.
+--------+ +------+ +-----+ +--------+ +------+ +-----+
| Client | | ACME | | DNS | | Client | | ACME | | DNS |
+--------+ +------+ +-----+ +--------+ +------+ +-----+
| | | | | |
STEP 1: Pre-Authorization of ancestor domain Step 1: Pre-authorization of ancestor domain.
| | | | | |
| POST /newAuthz | | | POST /newAuthz | |
| "example.org" | | | "example.org" | |
|--------------------------->| | |--------------------------->| |
| | | | | |
| 201 authorizations | | | 201 authorizations | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| Publish DNS TXT | | | Publish DNS TXT | |
| "example.org" | | | "example.org" | |
skipping to change at page 12, line 12 skipping to change at line 507
|--------------------------->| | |--------------------------->| |
| | Verify | | | Verify |
| |---------->| | |---------->|
| 200 status=valid | | | 200 status=valid | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| Delete DNS TXT | | | Delete DNS TXT | |
| "example.org" | | | "example.org" | |
|--------------------------------------->| |--------------------------------------->|
| | | | | |
STEP 2: Place order for sub1.example.org Step 2: Place order for sub1.example.org.
| | | | | |
| POST /newOrder | | | POST /newOrder | |
| "sub1.example.org" | | | "sub1.example.org" | |
|--------------------------->| | |--------------------------->| |
| | | | | |
| 201 status=ready | | | 201 status=ready | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| POST /finalize | | | POST /finalize | |
| CSR SAN "sub1.example.org" | | | CSR SAN "sub1.example.org" | |
skipping to change at page 12, line 35 skipping to change at line 530
| 200 OK status=valid | | | 200 OK status=valid | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| POST /certificate | | | POST /certificate | |
|--------------------------->| | |--------------------------->| |
| | | | | |
| 200 OK | | | 200 OK | |
| PEM SAN "sub1.example.org" | | | PEM SAN "sub1.example.org" | |
|<---------------------------| | |<---------------------------| |
| | | | | |
STEP 3: Place order for sub2.example.org Step 3: Place order for sub2.example.org.
| | | | | |
| POST /newOrder | | | POST /newOrder | |
| "sub2.example.org" | | | "sub2.example.org" | |
|--------------------------->| | |--------------------------->| |
| | | | | |
| 201 status=ready | | | 201 status=ready | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| POST /finalize | | | POST /finalize | |
| CSR SAN "sub2.example.org" | | | CSR SAN "sub2.example.org" | |
skipping to change at page 13, line 10 skipping to change at line 553
| 200 OK status=valid | | | 200 OK status=valid | |
|<---------------------------| | |<---------------------------| |
| | | | | |
| POST /certificate | | | POST /certificate | |
|--------------------------->| | |--------------------------->| |
| | | | | |
| 200 OK | | | 200 OK | |
| PEM SAN "sub2.example.org" | | | PEM SAN "sub2.example.org" | |
|<---------------------------| | |<---------------------------| |
* STEP 1: Pre-authorization of ancestor domain * Step 1: Pre-authorization of ancestor domain.
The client sends a newAuthz request for the ancestor domain The client sends a newAuthz request for the ancestor domain and
including the "subdomainAuthAllowed" flag in the identifier includes the subdomainAuthAllowed flag in the identifier object.
object.
POST /acme/new-authz HTTP/1.1 POST /acme/new-authz HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg", "kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "uQpSjlRb4vQVCjVYAyyUWg", "nonce": "uQpSjlRb4vQVCjVYAyyUWg",
skipping to change at page 13, line 37 skipping to change at line 579
"payload": base64url({ "payload": base64url({
"identifier": { "identifier": {
"type": "dns", "type": "dns",
"value": "example.org", "value": "example.org",
"subdomainAuthAllowed": true "subdomainAuthAllowed": true
} }
}), }),
"signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps" "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps"
} }
The server creates and returns an authorization object for the The server creates and returns an authorization object for the
identifier including the "subdomainAuthAllowed" flag. The object is identifier that includes the subdomainAuthAllowed flag. The
initially in "pending" state. object is initially in "pending" state.
{ {
"status": "pending", "status": "pending",
"expires": "2023-09-01T14:09:07.99Z", "expires": "2023-09-01T14:09:07.99Z",
"identifier": { "identifier": {
"type": "dns", "type": "dns",
"value": "example.org" "value": "example.org"
}, },
skipping to change at page 14, line 27 skipping to change at line 605
"type": "dns-01", "type": "dns-01",
"status": "pending", "status": "pending",
"token": "DGyRejmCefe7v4NfDGDKfA", "token": "DGyRejmCefe7v4NfDGDKfA",
"validated": "2023-08-01T12:05:58.16Z" "validated": "2023-08-01T12:05:58.16Z"
} }
], ],
"subdomainAuthAllowed": true "subdomainAuthAllowed": true
} }
The example illustrates the client completing a DNS challenge by The example illustrates the client completing a DNS challenge by
publishing a DNS TXT record. The client then posts to the challenge publishing a DNS TXT record. The client then posts to the
resource to inform the server that it can validate the challenge. challenge resource to inform the server that it can validate the
challenge.
Once the server validates the challenge by checking the DNS TXT Once the server validates the challenge by checking the DNS TXT
record, the server will transition the authorization object and record, the server will transition the authorization object and
associated challenge object status to "valid". associated challenge object status to "valid".
The call flow above illustrates the ACME server replying to the The call flow above illustrates the ACME server replying to the
client's challenge with status of "valid" after the ACME server has client's challenge with status of "valid" after the ACME server
validated the DNS challenge. However, the validation flow may take has validated the DNS challenge. However, the validation flow may
some time. If this is the case, the ACME server may reply to the take some time. If this is the case, the ACME server may reply to
client's challenge immediately with a status of "processing", and the the client's challenge immediately with a status of "processing"
client will then need to poll the authorization resource to see when and the client will then need to poll the authorization resource
it is finalized. Refer to ACME [RFC8555], Section 7.5.1 for more to see when it is finalized. Refer to Section 7.5.1 of [RFC8555]
details. for more details.
* STEP 2: The client places a newOrder for sub1.example.org * Step 2: The client places a newOrder for sub1.example.org.
The client sends a newOrder request to the server and includes the The client sends a newOrder request to the server and includes the
subdomain identifier. Note that the identifier is a subdomain of subdomain identifier. Note that the identifier is a subdomain of
the ancestor domain that has been pre-authorized in step 1. The the ancestor domain that has been pre-authorized in Step 1. The
client does not need to include the "subdomainAuthAllowed" field client does not need to include the subdomainAuthAllowed field in
in the "identifier" object as it has already pre-authorized the the identifier object, as it has already pre-authorized the
ancestor domain. ancestor domain.
POST /acme/new-order HTTP/1.1 POST /acme/new-order HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg", "kid": "https://example.com/acme/acct/evOfKhNU60wg",
skipping to change at page 15, line 26 skipping to change at line 653
"payload": base64url({ "payload": base64url({
"identifiers": [ "identifiers": [
{ "type": "dns", "value": "sub1.example.org" } { "type": "dns", "value": "sub1.example.org" }
], ],
"notBefore": "2023-09-01T00:04:00+04:00", "notBefore": "2023-09-01T00:04:00+04:00",
"notAfter": "2023-09-08T00:04:00+04:00" "notAfter": "2023-09-08T00:04:00+04:00"
}), }),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g" "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
} }
As an authorization object already exists for the ancestor domain, As an authorization object already exists for the ancestor domain,
the server replies with an order object with a status of "ready" that the server replies with an order object with a status of "ready"
includes a link to the existing "valid" authorization object. that includes a link to the existing "valid" authorization object.
HTTP/1.1 201 Created HTTP/1.1 201 Created
Replay-Nonce: MYAuvOpaoIiywTezizk5vw Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Link: <https://example.com/acme/directory>;rel="index" Link: <https://example.com/acme/directory>;rel="index"
Location: https://example.com/acme/order/TOlocE8rfgo Location: https://example.com/acme/order/TOlocE8rfgo
{ {
"status": "ready", "status": "ready",
"expires": "2023-09-01T14:09:07.99Z", "expires": "2023-09-01T14:09:07.99Z",
skipping to change at page 16, line 5 skipping to change at line 680
{ "type": "dns", "value": "sub1.example.org" } { "type": "dns", "value": "sub1.example.org" }
], ],
"authorizations": [ "authorizations": [
"https://example.com/acme/authz/PAniVnsZcis" "https://example.com/acme/authz/PAniVnsZcis"
], ],
"finalize": "https://example.com/acme/order/TOlocrfgo/finalize" "finalize": "https://example.com/acme/order/TOlocrfgo/finalize"
} }
The client can proceed to finalize the order by posting a CSR to the The client can proceed to finalize the order by posting a CSR to
"finalize" resource. The client can then download the certificate the finalize resource. The client can then download the
for sub1.example.org. certificate for sub1.example.org.
* STEP 3: The client places a newOrder for sub2.example.org * Step 3: The client places a newOrder for sub2.example.org.
The client sends a newOrder request to the server and includes the The client sends a newOrder request to the server and includes the
subdomain identifier. Note that the identifier is a subdomain of subdomain identifier. Note that the identifier is a subdomain of
the ancestor domain that has been pre-authorized in step 1. The the ancestor domain that has been pre-authorized in Step 1. The
client does not need to include the "subdomainAuthAllowed" field client does not need to include the subdomainAuthAllowed field in
in the "identifier" object as it has already pre-authorized the the identifier object, as it has already pre-authorized the
ancestor domain. ancestor domain.
POST /acme/new-order HTTP/1.1 POST /acme/new-order HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg", "kid": "https://example.com/acme/acct/evOfKhNU60wg",
skipping to change at page 16, line 39 skipping to change at line 714
"payload": base64url({ "payload": base64url({
"identifiers": [ "identifiers": [
{ "type": "dns", "value": "sub2.example.org" } { "type": "dns", "value": "sub2.example.org" }
], ],
"notBefore": "2023-09-01T00:04:00+04:00", "notBefore": "2023-09-01T00:04:00+04:00",
"notAfter": "2023-09-08T00:04:00+04:00" "notAfter": "2023-09-08T00:04:00+04:00"
}), }),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g" "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
} }
As an authorization object already exists for the ancestor domain, As an authorization object already exists for the ancestor domain,
the server replies with an order object with a status of "ready" that the server replies with an order object with a status of "ready"
includes a link to the existing "valid" authorization object. that includes a link to the existing "valid" authorization object.
HTTP/1.1 201 Created HTTP/1.1 201 Created
Replay-Nonce: MYAuvOpaoIiywTezizk5vw Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Link: <https://example.com/acme/directory>;rel="index" Link: <https://example.com/acme/directory>;rel="index"
Location: https://example.com/acme/order/TOlocE8rfgo Location: https://example.com/acme/order/TOlocE8rfgo
{ {
"status": "ready", "status": "ready",
"expires": "2023-09-01T14:09:07.99Z", "expires": "2023-09-01T14:09:07.99Z",
skipping to change at page 17, line 28 skipping to change at line 741
{ "type": "dns", "value": "sub2.example.org" } { "type": "dns", "value": "sub2.example.org" }
], ],
"authorizations": [ "authorizations": [
"https://example.com/acme/authz/PAniVnsZcis" "https://example.com/acme/authz/PAniVnsZcis"
], ],
"finalize": "https://example.com/acme/order/ROni7rdde/finalize" "finalize": "https://example.com/acme/order/ROni7rdde/finalize"
} }
The client can proceed to finalize the order by posting a CSR to the The client can proceed to finalize the order by posting a CSR to
"finalize" resource. The client can then download the certificate the finalize resource. The client can then download the
for sub2.example.org. certificate for sub2.example.org.
6. IANA Considerations 6. IANA Considerations
6.1. Authorization Object Fields Registry 6.1. Authorization Object Fields Registry
The following field is added to the "ACME Authorization Object The following field has been added to the "ACME Authorization Object
Fields" registry defined in ACME [RFC8555]. Fields" registry defined in ACME [RFC8555].
+----------------------+------------+--------------+-----------+ +======================+============+==============+===========+
| Field Name | Field Type | Configurable | Reference | | Field Name | Field Type | Configurable | Reference |
+----------------------+------------+--------------+-----------+ +======================+============+==============+===========+
| subdomainAuthAllowed | boolean | false | RFC XXXX | | subdomainAuthAllowed | boolean | false | RFC 9444 |
+----------------------+------------+--------------+-----------+ +----------------------+------------+--------------+-----------+
Table 1
6.2. Directory Object Metadata Fields Registry 6.2. Directory Object Metadata Fields Registry
The following field is added to the "ACME Directory Metadata Fields" The following field has been added to the "ACME Directory Metadata
registry defined in ACME [RFC8555]. Fields" registry defined in [RFC8555].
+----------------------+------------+-----------+ +======================+============+===========+
| Field Name | Field Type | Reference | | Field Name | Field Type | Reference |
+----------------------+------------+-----------+ +======================+============+===========+
| subdomainAuthAllowed | boolean | RFC XXXX | | subdomainAuthAllowed | boolean | RFC 9444 |
+----------------------+------------+-----------+ +----------------------+------------+-----------+
Table 2
7. Security Considerations 7. Security Considerations
This document specifies enhancements to ACME [RFC8555] that optimize This document specifies enhancements to ACME [RFC8555] that optimize
the protocol flows for issuance of certificates for subdomains. The the protocol flows for issuance of certificates for subdomains. The
underlying goal of ACME for Subdomains remains the same as that of underlying goal of ACME for Subdomains remains the same as that of
ACME: managing certificates that attest to identifier/key bindings ACME: managing certificates that attest to identifier/key bindings
for these subdomains. Thus, ACME for Subdomains has the same two for these subdomains. Thus, ACME for Subdomains has the same two
security goals as ACME: security goals as ACME:
1. Only an entity that controls an identifier can get an (1) Only an entity that controls an identifier can get an
authorization for that identifier authorization for that identifier.
2. Once authorized, an account key's authorizations cannot be (2) Once authorized, an account key's authorizations cannot be
improperly used by another account improperly used by another account.
ACME for Subdomains makes no changes to: ACME for Subdomains makes no changes to:
* account or account key management * account or account key management
* ACME channel establishment, security mechanisms or threat model * ACME channel establishment, security mechanisms, or threat model
* Validation channel establishment, security mechanisms or threat * validation channel establishment, security mechanisms, or threat
model model
Therefore, all Security Considerations in ACME in the following areas Therefore, all Security Considerations in ACME in the following areas
are equally applicable to ACME for Subdomains: are equally applicable to ACME for Subdomains:
* Threat Model * Threat Model
* Integrity of Authorizations * Integrity of Authorizations
* Denial-of-Service Considerations * Denial-of-Service Considerations
* Server-Side Request Forgery * Server-Side Request Forgery
* CA Policy Considerations * CA Policy Considerations
The only exception is that in order to satisfy goal (1) above, this The only exception is that in order to satisfy goal (1) above, this
draft assumes that control over a domain may imply control over a document assumes that control over a domain may imply control over a
subdomain, and therefore authorization for certificate issuance for subdomain; therefore, authorization for certificate issuance for the
the former may imply authorization for certificate issuance for the former may imply authorization for certificate issuance for the
latter. In many ecosystems, this is a safe assumption, especially latter. In many ecosystems, this is a safe assumption, especially
because control over the domain can often be leveraged to because control over the domain can often be leveraged to
successfully demonstrate control over subdomains anyway, for example successfully demonstrate control over subdomains anyway, for example,
by temporarily modifying DNS for the subdomain to point to a server by temporarily modifying DNS for the subdomain to point to a server
the ancestor domain owner controls, rendering the distinction moot. the ancestor domain owner controls, rendering the distinction moot.
For example, the CA/Browser Forum Baseline Requirements may consider For example, the CA/Browser Forum Baseline Requirements may consider
control of an ancestor domain sufficient for issuance of certificates control of an ancestor domain sufficient for issuance of certificates
for subdomains, but only if specific processes and procedures are for subdomains, but only if specific processes and procedures are
used for validating ownership of the ancestor domain. used for validating ownership of the ancestor domain.
In ecosystems where control of an ancestor domain may not imply In ecosystems where control of an ancestor domain may not imply
control over subdomains or authorization for issuance of certificates control over subdomains or authorization for issuance of certificates
for subdomains, a more complicated threat analysis and server policy for subdomains, a more complicated threat analysis and server policy
might be needed. might be needed.
Some additional comments on ACME server policy are given later in Some additional comments on ACME server policy are given later in
this section. this section.
7.1. Client Account Security 7.1. Client Account Security
There may be scenarios were a client wishes to deactivate an There may be scenarios were a client wishes to deactivate an
authorization object for an ancestor domain, or deactivate its authorization object for an ancestor domain or deactivate its account
account completely. For example, a client may want to do this if an completely. For example, a client may want to do this if an account
account key is compromised, or if a authorization object covering key is compromised or if an authorization object covering domains
domains subordinate to an ancestor domain is no longer needed. The subordinate to an ancestor domain is no longer needed. The client
client can deactivate an authorization using the mechanism specified can deactivate an authorization using the mechanism specified in
in [RFC8555], Section 7.5.2 and can deactivate an account using the [RFC8555], Section 7.5.2 and can deactivate an account using the
mechanism specified in [RFC8555], Section 7.3.6. mechanism specified in [RFC8555], Section 7.3.6.
7.2. Subdomain Determination 7.2. Subdomain Determination
The [RFC8499] definition of a subdomain is reproduced in Section 2. The [RFC8499] definition of a subdomain is reproduced in Section 2.
When comparing domains to determine if one is a subdomain of the When comparing domains to determine if one is a subdomain of the
other, it is important to compare entire labels, and not rely on a other, it is important to compare entire labels and not rely on a
string prefix match. Relying on string prefix matches may yield string prefix match. Relying on string prefix matches may yield
incorrect results. incorrect results.
7.3. ACME Server Policy Considerations 7.3. ACME Server Policy Considerations
The ACME for Subdomains and the ACME specifications do not mandate The ACME for Subdomains and the ACME specifications do not mandate
any specific ACME server or CA policies, or any specific use cases any specific ACME server or CA policies, or any specific use cases
for issuance of certificates. For example, an ACME server could be for issuance of certificates. For example, an ACME server could be
used: used:
* to issue Web PKI certificates where the ACME server must comply * to issue Web PKI certificates where the ACME server must comply
with CA/Browser Forum [CAB] Baseline Requirements. with CA/Browser Forum Baseline Requirements [CAB].
* as a Private CA for issuance of certificates within an * as a Private CA for issuance of certificates within an
organization. The organization could enforce whatever policies organization. The organization could enforce whatever policies
they desire on the ACME server. they desire on the ACME server.
* for issuance of IoT device certificates. There are currently no * for issuance of Internet of Things (IoT) device certificates.
IoT device certificate policies that are generally enforced across There are currently no IoT device certificate policies that are
the industry. Organizations issuing IoT device certificates can generally enforced across the industry. Organizations issuing IoT
enforce whatever policies they desire on the ACME server. device certificates can enforce whatever policies they desire on
the ACME server.
ACME server policy could specify whether: ACME server policy could specify whether:
* issuance of subdomain certificates is allowed based on proof of * issuance of subdomain certificates is allowed based on proof of
ownership of an ancestor domain ownership of an ancestor domain.
* issuance of subdomain certificates is allowed, but only for a * issuance of subdomain certificates is allowed, but only for a
specific set of ancestor domains specific set of ancestor domains.
* DNS based proof of ownership, or HTTP based proof of ownership, or * DNS-based or HTTP-based proof of ownership, or both, are allowed.
both, are allowed
The CA policy considerations listed in [RFC8555], Section 10.5 are The CA policy considerations listed in [RFC8555], Section 10.5 are
equally applicable here. These include, but are not limited to: equally applicable here. These include, but are not limited to:
* Is the claimed identifier syntactically valid? * Is the claimed identifier syntactically valid?
* For domain names: * For domain names:
* Is the name on the Public Suffix List? - Is the name on the Public Suffix List?
* Is the name a high-value name? - Is the name a high-value name?
* Is the key in the CSR sufficiently strong? * Is the key in the CSR sufficiently strong?
Refer to [RFC8555], Section 10.5 for more CA policy considerations. Refer to [RFC8555], Section 10.5 for more CA policy considerations.
ACME server policy specification is explicitly out of scope of this ACME server policy specification is explicitly out of scope of this
document. document.
8. References 8. References
skipping to change at page 21, line 21 skipping to change at line 924
January 2019, <https://www.rfc-editor.org/info/rfc8499>. January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. [RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019, (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>. <https://www.rfc-editor.org/info/rfc8555>.
8.2. Informative References 8.2. Informative References
[ACME-Identifier-Types] [ACME-Identifier-Types]
IANA, "ACME Identifier Types", n.d., IANA, "ACME Identifier Types",
<https://www.iana.org/assignments/acme/acme.xhtml#acme- <https://www.iana.org/assignments/acme/>.
identifier-types>.
[ACME-Validation-Methods] [ACME-Validation-Methods]
IANA, "ACME Validation Methods", n.d., IANA, "ACME Validation Methods",
<https://www.iana.org/assignments/acme/acme.xhtml#acme- <https://www.iana.org/assignments/acme/>.
validation-methods>.
[CAB] CA/Browser Forum, "Baseline Requirements for the Issuance [CAB] CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates", n.d., and Management of Publicly-Trusted Certificates",
<https://cabforum.org/baseline-requirements-documents/>. <https://cabforum.org/baseline-requirements-documents/>.
[RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for [RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for
Internet User Applications", RFC 819, Internet User Applications", RFC 819,
DOI 10.17487/RFC0819, August 1982, DOI 10.17487/RFC0819, August 1982,
<https://www.rfc-editor.org/info/rfc819>. <https://www.rfc-editor.org/info/rfc819>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
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