ACME for Subdomains
draft-ietf-acme-subdomains-03
The information below is for an old version of the document.
| Document | Type |
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| Authors | Owen Friel , Richard Barnes , Tim Hollebeek , Michael Richardson | ||
| Last updated | 2022-05-26 (Latest revision 2022-05-24) | ||
| Replaces | draft-friel-acme-subdomains | ||
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draft-ietf-acme-subdomains-03
ACME Working Group O. Friel
Internet-Draft R. Barnes
Intended status: Standards Track Cisco
Expires: 25 November 2022 T. Hollebeek
DigiCert
M. Richardson
Sandelman Software Works
24 May 2022
ACME for Subdomains
draft-ietf-acme-subdomains-03
Abstract
This document outlines how ACME can be used by a client to obtain a
certificate for a subdomain identifier from a certification
authority. The client has fulfilled a challenge against a parent
domain but does not need to fulfill a challenge against the explicit
subdomain as certification authority policy allows issuance of the
subdomain certificate without explicit subdomain ownership proof.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 November 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. ACME Workflow and Identifier Requirements . . . . . . . . . . 3
4. ACME Issuance of Subdomain Certificates . . . . . . . . . . . 5
4.1. Authorization Object . . . . . . . . . . . . . . . . . . 5
4.2. Pre-Authorization . . . . . . . . . . . . . . . . . . . . 6
4.3. New Orders . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Directory Object Metadata . . . . . . . . . . . . . . . . 9
5. Illustrative Call Flow . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. Authorization Object Fields Registry . . . . . . . . . . 15
6.2. Directory Object Metadata Fields Registry . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Subdomain Determination . . . . . . . . . . . . . . . . . 17
7.2. ACME Server Policy Considerations . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
ACME [RFC8555] defines a protocol that a certification authority (CA)
and an applicant can use to automate the process of domain name
ownership validation and X.509v3 (PKIX) [RFC5280] certificate
issuance. This document outlines how ACME can be used to issue
subdomain certificates, without requiring the ACME client to
explicitly fulfill an ownership challenge against the subdomain
identifiers - the ACME client need only fulfill an ownership
challenge against a parent domain identifier.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terms are defined in DNS Terminology [RFC8499] and are
reproduced here:
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* Label: An ordered list of zero or more octets that makes up a
portion of 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.
* Subdomain: "A domain is a subdomain of another domain if it is
contained within that domain. This relationship can be tested by
seeing if the subdomain's name ends with the containing domain's
name." (Quoted from [RFC1034], Section 3.1) For example, in the
host name "nnn.mmm.example.com", both "mmm.example.com" and
"nnn.mmm.example.com" are subdomains of "example.com". Note that
the comparisons here are done on whole labels; that is,
"ooo.example.com" is not a subdomain of "oo.example.com".
* Fully-Qualified Domain Name (FQDN): This is often just a clear way
of saying the same thing as "domain name of a node", as outlined
above. However, the term is ambiguous. Strictly speaking, a
fully-qualified domain name would include every label, including
the zero-length label of the root: such a name would be written
"www.example.net." (note the terminating dot). But, because every
name eventually shares the common root, names are often written
relative to the root (such as "www.example.net") and are still
called "fully qualified". This term first appeared in [RFC0819].
In this document, names are often written relative to the root.
The following additional terms are used in this document:
* Certification Authority (CA): An organization that is responsible
for the creation, issuance, revocation, and management of
Certificates. The term applies equally to both Root CAs and
Subordinate CAs
* CSR: Certificate Signing Request as defined in [RFC2986]
* Parent Domain: a domain is a parent domain of a subdomain if it
contains that subdomain, as per the [RFC8499] definition of
subdomain. For example, for the host name "nnn.mmm.example.com",
both "mmm.example.com" and "example.com" are parent domains of
"nnn.mmm.example.com". Note that the comparisons here are done on
whole labels; that is, "oo.example.com" is not a parent domain of
"ooo.example.com"
3. ACME Workflow and Identifier Requirements
A typical ACME workflow for issuance of certificates is as follows:
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1. client POSTs a newOrder request that contains a set of
"identifiers"
2. server replies with a set of "authorizations" and a "finalize"
URI
3. client sends POST-as-GET requests to retrieve the
"authorizations", with the downloaded "authorization" object(s)
containing the "identifier" that the client must prove that they
control, and a set of associated "challenges", one of which the
client must fulfill
4. client proves control over the "identifier" in the
"authorization" object by completing one of the specified
challenges, for example, by publishing a DNS TXT record
5. client POSTs a CSR to the "finalize" API
6. server replies with an updated order object that includes a
"certificate" URI
7. client sends POST-as-GET request to the "certificate" URI to
download the certificate
ACME places the following restrictions on "identifiers":
* [RFC8555] section 7.1.3: The authorizations required are dictated
by server policy; there may not be a 1:1 relationship between the
order identifiers and the authorizations required.
* [RFC8555] section 7.1.4: the only type of "identifier" defined by
the ACME specification is an FQDN: "The only type of identifier
defined by this specification is a fully qualified domain name
(type: "dns"). The domain name MUST be encoded in the form in
which it would appear in a certificate."
* [RFC8555] section 7.4: the "identifier" in the CSR request must
match the "identifier" in the newOrder request: "The CSR MUST
indicate the exact same set of requested identifiers as the
initial newOrder request."
* [RFC8555] section 8.3: the "identifier", or FQDN, in the
"authorization" object must be used when fulfilling challenges via
HTTP: "Construct a URL by populating the URL template ... where
the domain field is set to the domain name being verified"
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* [RFC8555] section 8.4: the "identifier", or FQDN, in the
"authorization" object must be used when fulfilling challenges via
DNS: "The client constructs the validation domain name by
prepending the label "_acme-challenge" to the domain name being
validated."
ACME does not mandate that the "identifier" in a newOrder request
matches the "identifier" in "authorization" objects.
4. ACME Issuance of Subdomain Certificates
As noted in the previous section, ACME does not mandate that the
"identifier" in a newOrder request matches the "identifier" in
"authorization" objects. This means that the ACME specification does
not preclude an ACME server processing newOrder requests and issuing
certificates for a subdomain without requiring a challenge to be
fulfilled against that explicit subdomain.
ACME server policy could allow issuance of certificates for a
subdomain to a client where the client only has to fulfill an
authorization challenge for a parent domain of that subdomain. This
allows a flow where a client proves ownership of, for example,
"example.org" and then successfully obtains a certificate for
"sub.example.org".
ACME server policy is out of scope of this document, however, some
commentary is provided in Section 7.2.
Clients need a mechanism to instruct the ACME server that they are
requesting authorization for all subdomains subordinate to the
specified domain, as opposed to just requesting authorization for an
explicit domain identifier. Clients need a mechanism to do this in
both newAuthz and newOrder requests. ACME servers need a mechanism
to indicate to clients that authorization objects are valid for all
subdomains under the specified domain. These are described in this
section.
4.1. Authorization Object
ACME [RFC8555] section 7.1.4 defines the authorization object. When
ACME server policy allows authorization for subdomains subordinate to
a domain, the server indicates this by including the
"subdomainAuthAllowed" flag in the authorization object for that
domain identifier:
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subdomainAuthAllowed (optional, boolean): This field MUST be
present and true for authorizations where ACME server policy
allows certificates to be issued for any subdomain subordinate
to the domain specified in the 'identifier' field of the
authorization object.
The following example shows an authorization object for the domain
example.org where the authorization covers the subdomains subordinate
to example.org.
{
"status": "valid",
"expires": "2015-03-01T14:09:07.99Z",
"identifier": {
"type": "dns",
"value": "example.org"
},
"challenges": [
{
"url": "https://example.com/acme/chall/prV_B7yEyA4",
"type": "http-01",
"status": "valid",
"token": "DGyRejmCefe7v4NfDGDKfA",
"validated": "2014-12-01T12:05:58.16Z"
}
],
"subdomainAuthAllowed": true
}
If the "subdomainAuthAllowed" field is not included, then the assumed
default value is false.
4.2. Pre-Authorization
The standard ACME workflow has authorization objects created
reactively in response to a certificate order. ACME also allows for
pre-authorization, where clients obtain authorization for an
identifier proactively, outside of the context of a specific
issuance. With the ACME pre-authorization flow, a client can pre-
authorize for a domain once, and then issue multiple newOrder
requests for certificates with identifiers in the subdomains
subordinate to that domain.
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ACME [RFC8555] section 7.4.1 defines the "identifier" object for
newAuthz requests. One additional field for the "identifier" object
is defined:
subdomainAuthAllowed (optional, boolean): An ACME client sets
this flag to indicate to the server that it is requesting an
authorization for the subdomains subordinate to the specified
domain identifier value
Clients include the flag in the "identifier" object of newAuthz
requests to indicate that they are requesting a subdomain
authorization. In the following example newAuthz payload, the client
is requesting pre-authorization for the subdomains subordinate to
example.org.
"payload": base64url({
"identifier": {
"type": "dns",
"value": "example.org",
"subdomainAuthAllowed": true
}
})
If the server is willing to allow a single authorization for the
subdomains, and there is not an existing authorization object for the
identifier, then it will create an authorization object and include
the "subdomainAuthAllowed" flag with value of true. If the server
policy does not allow creation of subdomain authorizations
subordinate to that domain, the server can create an authorization
object for the indicated identifier, and include the
"subdomainAuthAllowed" flag with value of false. In both scenarios,
handling of the pre-authorization follows the process documented in
ACME section 7.4.1.
4.3. New Orders
Clients need a mechanism to optionally indicate to servers whether or
not they are authorized to fulfill challenges against parent domains
for a given identifier FQDN. For example, if a client places an
order for an identifier foo.bar.example.org, and is authorized to
fulfill a challenge against the parent domains bar.example.org or
example.org, then the client needs a mechanism to indicate control
over the parent domains to the ACME server.
This can be achieved by adding an optional field "parentDomain" to
the "identifiers" field in the order object:
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parentDomain (optional, string): This is a parent domain of
the requested identifier. The client MUST be able to fulfill
a challenge against the parent domain.
This field specifies a parent domain of the identifier that the
client has DNS control over, and is capable of fulfilling challenges
against. Based on server policy, the server can choose to issue a
challenge against any parent domain of the identifier up to and
including the specified "parentDomain", and create a corresponding
authorization object against the chosen identifier.
In the following example newOrder payload, the client requests a
certificate for identifier foo.bar.example.org and indicates that it
can fulfill a challenge against the parent domain bar.example.org.
The server can then choose to issue a challenge against either
foo.bar.example.org or bar.example.org identifiers.
"payload": base64url({
"identifiers": [
{ "type": "dns",
"value": "foo.bar.example.org",
"parentDomain": "bar.example.org" }
],
"notBefore": "2016-01-01T00:04:00+04:00",
"notAfter": "2016-01-08T00:04:00+04:00"
})
In the following example newOrder payload, the client requests a
certificate for identifier foo.bar.example.org and indicates that it
can fulfill a challenge against the parent domain example.org. The
server can then choose to issue a challenge against any one of
foo.bar.example.org, bar.example.org or example.org identifiers.
"payload": base64url({
"identifiers": [
{ "type": "dns",
"value": "foo.bar.example.org",
"parentDomain": "example.org" }
],
"notBefore": "2016-01-01T00:04:00+04:00",
"notAfter": "2016-01-08T00:04:00+04:00"
})
If the client is unable to fulfill authorizations against parent
domain, the client should not include the "parentDomain" field.
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Server newOrder handling generally follows the process documented
ACME section 7.4. If the server is willing to allow subdomain
authorizations for the domain specified in "parentDomain", then it
creates an authorization object against that parent domain and
includes the "subdomainAuthAllowed" flag with a value of true. If
the server policy does not allow creation of subdomain authorizations
against that parent domain, then it can create an authorization
object for the indicated identifier value, and includes the
"subdomainAuthAllowed" flag with value of false.
4.4. Directory Object Metadata
An ACME server can advertise support for authorization of subdomains
by including the following boolean flag in its "ACME Directory
Metadata Fields" registry:
subdomainAuthAllowed (optional, bool): Indicates if an ACME
server supports authorization of subdomains.
If not specified, then no default value is assumed. If an ACME
server supports authorization of subdomains, it can indicate this by
including this field with a value of "true".
5. Illustrative Call Flow
The call flow illustrated here uses the ACME pre-authorization flow
using DNS-based proof of ownership.
+--------+ +------+ +-----+
| Client | | ACME | | DNS |
+--------+ +------+ +-----+
| | |
STEP 1: Pre-Authorization of parent domain
| | |
| POST /newAuthz | |
| "example.org" | |
|--------------------------->| |
| | |
| 201 authorizations | |
|<---------------------------| |
| | |
| Publish DNS TXT | |
| "example.org" | |
|--------------------------------------->|
| | |
| POST /challenge | |
|--------------------------->| |
| | Verify |
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| |---------->|
| 200 status=valid | |
|<---------------------------| |
| | |
| Delete DNS TXT | |
| "example.org" | |
|--------------------------------------->|
| | |
STEP 2: Place order for sub1.example.org
| | |
| POST /newOrder | |
| "sub1.example.org" | |
|--------------------------->| |
| | |
| 201 status=ready | |
|<---------------------------| |
| | |
| POST /finalize | |
| CSR SAN "sub1.example.org" | |
|--------------------------->| |
| | |
| 200 OK status=valid | |
|<---------------------------| |
| | |
| POST /certificate | |
|--------------------------->| |
| | |
| 200 OK | |
| PEM SAN "sub1.example.org" | |
|<---------------------------| |
| | |
STEP 3: Place order for sub2.example.org
| | |
| POST /newOrder | |
| "sub2.example.org" | |
|--------------------------->| |
| | |
| 201 status=ready | |
|<---------------------------| |
| | |
| POST /finalize | |
| CSR SAN "sub2.example.org" | |
|--------------------------->| |
| | |
| 200 OK status=valid | |
|<---------------------------| |
| | |
| POST /certificate | |
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|--------------------------->| |
| | |
| 200 OK | |
| PEM SAN "sub2.example.org" | |
|<---------------------------| |
* STEP 1: Pre-authorization of parent domain
The client sends a newAuthz request for the parent domain
including the "subdomainAuthAllowed" flag in the identifier
object.
POST /acme/new-authz HTTP/1.1
Host: example.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "uQpSjlRb4vQVCjVYAyyUWg",
"url": "https://example.com/acme/new-authz"
}),
"payload": base64url({
"identifier": {
"type": "dns",
"value": "example.org",
"subdomainAuthAllowed": true
}
}),
"signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps"
}
The server creates and returns an authorization object for the
identifier including the "subdomainAuthAllowed" flag. The object is
initially in "pending" state.
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{
"status": "pending",
"expires": "2015-03-01T14:09:07.99Z",
"identifier": {
"type": "dns",
"value": "example.org"
},
"challenges": [
{
"url": "https://example.com/acme/chall/prV_B7yEyA4",
"type": "http-01",
"status": "pending",
"token": "DGyRejmCefe7v4NfDGDKfA",
"validated": "2014-12-01T12:05:58.16Z"
}
],
"subdomainAuthAllowed": true
}
Once the client completes the challenge, the server will transition
the authorization object and associated challenge object status to
"valid". The call flow above illustrates the ACME server replying to
the client's challenge with status of "valid" after the ACME server
has validated the DNS challenge.
However, the validation flow may take some time. If this is the
case, the ACME server may reply to the client's challenge immediately
with a status of "processing", and the client will then need to poll
the authorization resource to see when it is finalized. Refer to
ACME [RFC8555] section 7.5.1 for more details.
* STEP 2: The client places a newOrder for sub1.example.org
The client sends a newOrder request to the server and includes the
subdomain identifier. Note that the identifier is a subdomain of
the parent domain that has been pre-authorised in step 1. The
client does not need to include the "subdomainAuthAllowed" field
in the "identifier" object as it has already pre-authorized the
parent domain.
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POST /acme/new-order HTTP/1.1
Host: example.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "5XJ1L3lEkMG7tR6pA00clA",
"url": "https://example.com/acme/new-order"
}),
"payload": base64url({
"identifiers": [
{ "type": "dns", "value": "sub1.example.org" }
],
"notBefore": "2016-01-01T00:04:00+04:00",
"notAfter": "2016-01-08T00:04:00+04:00"
}),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
}
As an authorization object already exists for the parent domain, the
server replies with an order object with a status of "ready" that
includes a link to the existing "valid" authorization object.
HTTP/1.1 201 Created
Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Link: <https://example.com/acme/directory>;rel="index"
Location: https://example.com/acme/order/TOlocE8rfgo
{
"status": "ready",
"expires": "2016-01-05T14:09:07.99Z",
"notBefore": "2016-01-01T00:00:00Z",
"notAfter": "2016-01-08T00:00:00Z",
"identifiers": [
{ "type": "dns", "value": "sub1.example.org" }
],
"authorizations": [
"https://example.com/acme/authz/PAniVnsZcis"
],
"finalize": "https://example.com/acme/order/TOlocrfgo/finalize"
}
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The client can proceed to finalize the order and download the
certificate for sub1.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
subdomain identifier. Note that the identifier is a subdomain of
the parent domain that has been pre-authorised in step 1. The
client does not need to include the "subdomainAuthAllowed" field
in the "identifier" object as it has already pre-authorized the
parent domain.
POST /acme/new-order HTTP/1.1
Host: example.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/evOfKhNU60wg",
"nonce": "5XJ1L3lEkMG7tR6pA00clA",
"url": "https://example.com/acme/new-order"
}),
"payload": base64url({
"identifiers": [
{ "type": "dns", "value": "sub2.example.org" }
],
"notBefore": "2016-01-01T00:04:00+04:00",
"notAfter": "2016-01-08T00:04:00+04:00"
}),
"signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
}
As an authorization object already exists for the parent domain, the
server replies with an order object with a status of "ready" that
includes a link to the existing "valid" authorization object.
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HTTP/1.1 201 Created
Replay-Nonce: MYAuvOpaoIiywTezizk5vw
Link: <https://example.com/acme/directory>;rel="index"
Location: https://example.com/acme/order/TOlocE8rfgo
{
"status": "ready",
"expires": "2016-01-05T14:09:07.99Z",
"notBefore": "2016-01-01T00:00:00Z",
"notAfter": "2016-01-08T00:00:00Z",
"identifiers": [
{ "type": "dns", "value": "sub2.example.org" }
],
"authorizations": [
"https://example.com/acme/authz/PAniVnsZcis"
],
"finalize": "https://example.com/acme/order/ROni7rdde/finalize"
}
The client can proceed to finalize the order and download the
certificate for sub2.example.org.
6. IANA Considerations
6.1. Authorization Object Fields Registry
The following field is added to the "ACME Authorization Object
Fields" registry defined in ACME [RFC8555].
+----------------------+------------+--------------+-----------+
| Field Name | Field Type | Configurable | Reference |
+----------------------+------------+--------------+-----------+
| subdomainAuthAllowed | boolean | false | RFC XXXX |
+----------------------+------------+--------------+-----------+
6.2. Directory Object Metadata Fields Registry
The following field is added to the "ACME Directory Metadata Fields"
registry defined in ACME [RFC8555].
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+----------------------+------------+-----------+
| Field Name | Field Type | Reference |
+----------------------+------------+-----------+
| subdomainAuthAllowed | boolean | RFC XXXX |
+----------------------+------------+-----------+
7. Security Considerations
This document documents enhancements to ACME [RFC8555] that optimize
the protocol flows for issuance of certificates for subdomains. The
underlying goal of ACME for Subdomains remains the same as that of
ACME: managing certificates that attest to identifier/key bindings
for these subdomains. Thus, ACME for Subdomains has the same two
security goals as ACME:
1. Only an entity that controls an identifier can get an
authorization for that identifier
2. Once authorized, an account key's authorizations cannot be
improperly used by another account
ACME for Subdomains makes no changes to:
* account or account key management
* ACME channel establishment, security mechanisms or threat model
* Validation channel establishment, security mechanisms or threat
model
Therefore, all Security Considerations in ACME in the following areas
are equally applicable to ACME for Subdomains:
* Threat Model
* Integrity of Authorizations
* Denial-of-Service Considerations
* Server-Side Request Forgery
* CA Policy Considerations
Some additional comments on ACME server policy are given in the
following section.
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7.1. Subdomain Determination
The [RFC8499] definition of a subdomain is reproduced in Section 2.
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
string prefix match. Relying on string prefix matches may yield
incorrect results.
7.2. ACME Server Policy Considerations
The ACME for Subdomains and the ACME specifications do not mandate
any specific ACME server or CA policies, or any specific use cases
for issuance of certificates. For example, an ACME server could be
used:
* to issue Web PKI certificates where the ACME server must comply
with CA/Browser Forum [CAB] Baseline Requirements.
* as a Private CA for issuance of certificates within an
organization. The organization could enforce whatever policies
they desire on the ACME server.
* for issuance of IoT device certificates. There are currently no
IoT device certificate policies that are generally enforced across
the industry. Organizations issuing IoT device certificates can
enforce whatever policies they desire on the ACME server.
ACME server policy could specify whether:
* issuance of subdomain certificates is allowed based on proof of
ownership of a parent domain
* issuance of subdomain certificates is allowed, but only for a
specific set of parent domains
* whether DNS based proof of ownership, or HTTP based proof of
ownership, or both, are allowed
ACME server policy specification is explicitly out of scope of this
document.
8. References
8.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[CAB] CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates", n.d.,
<https://cabforum.org/wp-content/uploads/CA-Browser-Forum-
BR-1.7.1.pdf>.
[RFC0819] Su, Z. and J. Postel, "The Domain Naming Convention for
Internet User Applications", RFC 819,
DOI 10.17487/RFC0819, August 1982,
<https://www.rfc-editor.org/info/rfc819>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
Authors' Addresses
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Owen Friel
Cisco
Email: ofriel@cisco.com
Richard Barnes
Cisco
Email: rlb@ipv.sx
Tim Hollebeek
DigiCert
Email: tim.hollebeek@digicert.com
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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