| Security Events Working Group | A. Backman, Ed. |
| Internet-Draft | Amazon |
| Intended status: Standards Track | M. Scurtescu |
| Expires: January 9, 2020 | Coinbase |
| July 08, 2019 |
Subject Identifiers for Security Event Tokens
draft-ietf-secevent-subject-identifiers-04
Security events communicated within Security Event Tokens may support a variety of identifiers to identify the subject and/or other principals related to the event. This specification formalizes the notion of subject identifiers as named sets of well-defined claims describing the subject, a mechanism for representing subject identifiers within a [JSON] object such as a JSON Web Token or Security Event Token, and a registry for defining and allocating names for these claim sets.
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As described in section 1.2 of [SET], the subject of a security event may take a variety of forms, including but not limited to a JWT principal, an IP address, a URL, etc. Furthermore, even in the case where the subject of an event is more narrowly scoped, there may be multiple ways by which a given subject may be identified. For example, an account may be identified by an opaque identifier, an email address, a phone number, a JWT iss claim and sub claim, etc., depending on the nature and needs of the transmitter and receiver. Even within the context of a given transmitter and receiver relationship, it may be appropriate to identify different accounts in different ways, for example if some accounts only have email addresses associated with them while others only have phone numbers. Therefore it can be necessary to indicate within a SET the mechanism by which the subject of the security event is being identified.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].
A Subject Identifier Type is a light-weight schema that describes a set of claims that identifies a subject. Every Subject Identifier Type MUST have a unique name registered in the IANA “Security Event Subject Identifier Types” registry established by Section 7.1. A Subject Identifier Type MAY describe more claims than are strictly necessary to identify a subject, and MAY describe conditions under which those claims are required, optional, or prohibited.
A Subject Identifier is a [JSON] object containing a subject_type claim whose value is the name of a Subject Identifier Type, and a set of additional “payload claims” which are to be interpreted according to the rules defined by that Subject Identifier Type. Payload claim values MUST match the format specified for the claim by the Subject Identifier Type. A Subject Identifier MUST NOT contain any payload claims prohibited or not described by its Subject Identifier Type, and MUST contain all payload claims required by its Subject Identifier Type.
The following Subject Identifier Types are registered in the IANA “Security Event Subject Identifier Types” registry established by Section 7.1.
The Account Subject Identifier Type describes a user account at a service provider, identified with an acct URI as defined in [RFC7565]. Subject Identifiers of this type MUST contain a uri claim whose value is the acct URI for the subject. The uri claim is REQUIRED and MUST NOT be null or empty. The Account Subject Identifier Type is identified by the name account.
Below is a non-normative example Subject Identifier for the Account Subject Identifier Type:
{
"subject_type": "account",
"uri": "acct:example.user@service.example.com",
}
Figure 1: Example: Subject Identifier for the Account Subject Identifier Type.
The Email Subject Identifier Type describes a principal identified with an email address. Subject Identifiers of this type MUST contain an email claim whose value is a string containing the email address of the subject, formatted as an addr-spec as defined in Section 3.4.1 of [RFC5322]. The email claim is REQUIRED and MUST NOT be null or empty. The value of the email claim SHOULD identify a mailbox to which email may be delivered, in accordance with [RFC5321]. The Email Subject Identifier Type is identified by the name email.
Below is a non-normative example Subject Identifier for the Email Subject Identifier Type:
{
"subject_type": "email",
"email": "user@example.com",
}
Figure 2: Example: Subject Identifier for the Email Subject Identifier Type.
Many email providers will treat multiple email addresses as equivalent. For example, some providers treat email addresses as case-insensitive, and consider “user@example.com”, “User@example.com”, and “USER@example.com” as the same email address. This has led users to view these strings as equivalent, driving service providers to implement proprietary email canonicalization algorithms to ensure that email addresses entered by users resolve to the same canonical string. When receiving an Email Subject Identifier, the recipient SHOULD use their implementation’s canonicalization algorithm to resolve the email address to the same subject identifier string used in their system.
The Phone Number Subject Identifier Type describes a principal identified with a telephone number. Subject Identifiers of this type MUST contain a phone claim whose value is a string containing the full telephone number of the subject, including international dialing prefix, formatted according to E.164. The phone claim is REQUIRED and MUST NOT be null or empty. The Phone Number Subject Identifier Type is identified by the name phone.
Below is a non-normative example Subject Identifier for the Email Subject Identifier Type:
{
"subject_type": "phone",
"phone": "+12065550100",
}
Figure 3: Example: Subject Identifier for the Phone Number Subject Identifier Type.
The Issuer and Subject Subject Identifier Type describes a principal identified with a pair of iss and sub claims, as defined by [JWT]. These claims MUST follow the formats of the iss claim and sub claim defined by [JWT], respectively. Both the iss claim and the sub claim are REQUIRED and MUST NOT be null or empty. The Issuer and Subject Subject Identifier Type is identified by the name iss-sub.
Below is a non-normative example Subject Identifier for the Issuer and Subject Subject Identifier Type:
{
"subject_type": "iss-sub",
"iss": "http://issuer.example.com/",
"sub": "145234573",
}
Figure 4: Example: Subject Identifier for the Issuer and Subject Subject Identifier Type.
The Aliases Subject Identifier Type describes a subject that is identified with a list of different Subject Identifiers. It is intended for use when a variety of identifiers have been shared with the party that will be interpreting the Subject Identifier, and it is unknown which of those identifiers they will recognize or support. Subject Identifiers of this type MUST contain an identifiers claim whose value is a JSON array containing one or more Subject Identifiers. Each Subject Identifier in the array MUST identify the same entity. The identifiers claim is REQUIRED and MUST NOT be null or empty. It MAY contain multiple instances of the same Subject Identifier Type (e.g., multiple Email Subject Identifiers), but SHOULD NOT contain exact duplicates. This type is identified by the name aliases.
alias Subject Identifiers MUST NOT be nested; i.e., the identifiers claim of an alias Subject Identifier MUST NOT contain a Subject Identifier of type aliases.
Below is a non-normative example Subject Identifier for the Aliases Subject Identifier Type:
{
"subject_type": "aliases",
"identifiers": [
{
"subject_type": "email",
"email": "user@example.com",
},
{
"subject_type": "phone",
"phone": "+12065550100",
},
{
"subject_type": "email",
"email": "user+qualifier@example.com",
}
],
}
Figure 5: Example: Subject Identifier for the Aliases Subject Identifier Type.
This document defines the sub_id JWT Claim, in accordance with Section 4.2 of [RFC7519]. When present, the value of this claim MUST be a Subject Identifier that identifies the principal that is the subject of the JWT. The sub_id claim MAY be included in a JWT, whether or not the sub claim is present. When both the sub and sub_id claims are present in a JWT, they MUST identify the same principal.
Below is are non-normative examples of JWTs containing the sub_id claim:
{
"iss": "issuer.example.com",
"sub_id": {
"subject_type": "email",
"email": "user@example.com",
},
}
Figure 6: Example: JWT containing a `sub_id` claim and no `sub` claim.
{
"iss": "issuer.example.com",
"sub": "user@example.com",
"sub_id": {
"subject_type": "email",
"email": "user@example.com",
},
}
Figure 7: Example: JWT where both the `sub` and `sub_id` claims identify the subject using the same identifier.
{
"iss": "issuer.example.com",
"sub": "user@example.com",
"sub_id": {
"subject_type": "email",
"email": "elizabeth@example.com",
},
}
Figure 8: Example: JWT where both the `sub` and `sub_id` claims identify the subject using different values of the same identifier type.
{
"iss": "issuer.example.com",
"sub": "user@example.com",
"sub_id": {
"subject_type": "account",
"uri": "acct:example.user@service.example.com",
},
}
Figure 9: Example: JWT where the `sub` and `sub_id` claims identify the subject via different types of identifiers.
The sub_id claim MAY contain an iss-sub Subject Identifier. In this case, the JWT’s iss claim and the Subject Identifier’s iss claim MAY be different. For example, an OpenID Connect client may construct such a JWT when issuing a JWT back to its OpenID Connect Identity Provider, in order to communicate information about the services’ shared subject principal using an identifier the Identity Provider is known to understand. Similarly, the JWT’s sub claim and the Subject Identifier’s sub claim MAY be different. For example, this may be used by an OpenID Connect client to communicate the subject principal’s local identifier at the client back to its Identity Provider.
Below are non-normative examples of a JWT where the iss claims are the same, and a JWT where they are different.
{
"iss": "issuer.example.com",
"sub_id": {
"subject_type": "iss-sub",
"iss": "issuer.example.com",
"sub": "example_user",
},
}
Figure 10: Example: JWT with a `iss-sub` Subject Identifier where JWT issuer and subject issuer are the same.
{
"iss": "client.example.com",
"sub_id": {
"subject_type": "iss-sub",
"iss": "issuer.example.com",
"sub": "example_user",
},
}
Figure 11: Example: JWT with an `iss-sub` Subject Identifier where the JWT issuer and subject issuer are different.
{
"iss": "client.example.com",
"sub": "client_user",
"sub_id": {
"subject_type": "iss-sub",
"iss": "issuer.example.com",
"sub": "example_user",
},
}
Figure 12: Example: JWT with an `iss-sub` Subject Identifier where the JWT `iss` and `sub` claims differ from the Subject Identifier's `iss` and `sub` claims.
The act of presenting two or more identifiers for a single principal together (e.g., within an aliases Subject Identifier, or via the sub and sub_id JWT claims) may communicate more information about the principal than was intended. For example, the entity to which the identifiers are presented, now knows that both identifiers relate to the same principal, and may be able to correlate additional data based on that. When transmitting Subject Identifiers, the transmitter SHOULD take care that they are only transmitting multiple identifiers together when it is known that the recipient already knows that the identifiers are related (e.g., because they were previously sent to the recipient as claims in an OpenID Connect ID Token).
There are no security considerations.
This document defines Subject Identifier Types, for which IANA is asked to create and maintain a new registry titled “Security Event Subject Identifier Types”. Initial values for the Security Event Subject Identifier Types registry are given in Section 3. Future assignments are to be made through the Expert Review registration policy [BCP26] and shall follow the template presented in Section 7.1.1.
The Expert Reviewer is expected to review the documentation referenced in a registration request to verify its completeness. The Expert Reviewer must base their decision to accept or reject the request on a fair and impartial assessment of the request. If the Expert Reviewer has a conflict of interest, such as being an author of a defining document referenced by the request, they must recuse themselves from the approval process for that request. In the case where a request is rejected, the Expert Reviewer should provide the requesting party with a written statement expressing the reason for rejection, and be prepared to cite any sources of information that went into that decision.
Subject Identifier Types need not be generally applicable and may be highly specific to a particular domain; it is expected that types may be registered for niche or industry-specific use cases. The Expert Reviewer should focus on whether the type is thoroughly documented, and whether its registration will promote or harm interoperability. In most cases, the Expert Reviewer should not approve a request if the registration would contribute to confusion, or amount to a synonym for an existing type.
This document defines the sub_id JWT Claim, which IANA is asked to register in the “JSON Web Token Claims” registry IANA JSON Web Token Claims Registry established by [SET].
| [OIDC] | Sakimura, N., Bradley, J., Jones, M., de Medeiros, B. and C. Mortimore, "OpenID Connect Core 1.0", November 2014. |
This document is based on work developed within the OpenID RISC Working Group. The authors would like to thank the members of this group for their hard work and contributions.
(This section to be removed by the RFC Editor before publication as an RFC.)
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