Multi-Subject JSON Web Token (JWT)

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Table of Contents

1. Introduction

JSON Web Token (JWT) [RFC7519] is a mechanism that is used to transfer claims between two parties across security domains. Nested JWT is a JWT in which the payload is another JWT. The current specification does not define a means by which the enclosing JWT could have its own Claims Set, only the enclosed JWT would have claims.¶

There are a number of use cases where there is a need to represent multiple related subjects in one JWT; a primary subject and a related secondary subject.¶

This specification defines a mechanism for including multiple subjects in a JWT. A primary subject in an enclosing JWT with its own claims, and a related secondary subject in a nested JWT with its own claims.¶

2. Use Cases

The following are few use cases that might benefit from such a concept, that fall into two different categories:¶

3. Authorization Request

To allow the AS to differentiate between an authorization request for a single subject and an authorization request for multiple subjects, this document defines the following parameter:¶

issuer-hint:

A hint to the AS that the request is for a multi-subject token, which can take one of two values:¶

Internal

Indicates that the AS handling the current request will be issuing both enclosing and enclosed JWTs.¶

External

Indicates that an external entity has issued the JWT to be enclosed, which will be carried in access_token parameter.¶

If the access_token query parameter is included in the request, then the AS SHOULD embed the provided token in the issued token, if the issuer-hint has the "External" value.¶

4. JWT Content

The payload of the enclosing JWT is JSON object that contains the Claims Set of the primary subject, and one new claim that is used to hold the enclosed JWT and its relation to the primary subject.¶

This document defines a new claim, "rsub" (Related Subject) Claim, that is used to contain the enclosed JWT and its relation to the primary subject. The "rsub" contains two claims:¶

rel:

Defines the relationship between the enclosed JWT and the enclosing JWT. It can take one of the values defined in section Section 5¶

jwt:

Contains the enclosed JWT.¶

5. Token Relationship

The following relathionship types are defined by this specification:¶

urn:ietf:params:oauth:subject-type:authority

Indicates that the subject in the enclosed JWT has authority over the subject in the enclosing JWT.¶

This URN could be used in the child/parent use case described in Section 2.1.1.¶

urn:ietf:params:oauth:subject-type:primary

Indicates that the subject in the enclosed JWT is related primary subject¶

This URN could be used in the married couple use case described in Section 2.1.2.¶

urn:ietf:params:oauth:subject-type:actor

Indicates that the subject in the enclosed JWT is acting on behalf of the primary subject¶

This URN could be used in the delegation use case described in Section 2.1.3.¶

urn:ietf:params:oauth:subject-type:original

Indicates that the subject in the enclosed JWT is the original JWT that resulted in the primary subject JWT¶

This URN could be used in all the use cases described in Section 2.2.¶

6. Example

The following example is for a multi-subject token that represents a child/parent relashionship. The enclosing JWT represents the primary user, the child in this case, and the enclosed token in the "rsub" claim represents the secondary user, the parent in this case.¶

{
  "alg": "HS256",
  "typ": "JWT",
}
{
   "sub": "1234567890",
   "name": "John Doe",
   "iat": 1516239022,
   "rsub": {
      “rel” :  "urn:ietf:params:oauth:subject-type:authority"
      “jwt” : {
         "sub": "9876543210",
         "name": "Alice Doe",
         "iat": 1516239022,
      }
   }
}

In this use case, both JWTs are issued by the same entity handling the authorization request.¶

7. Security Considerations

The existing security considerations apply to the use cases where the JWTs are issued by the same entity. Allowing more than one subject to access the same account might open the door for potential abuse. Care must be taken to ensure that when a secondary subject is added to an account that an adequate approval process is in place.¶

In the multiple issuers use cases, the entity handling the incoming authorization request that contains a JWT MUST validate the token and ensure that it is coming from a trusted entity, before attempting to embed that JWT into a new multi-subject JWT issued by the AS.¶

8. IANA Considerations

TODO¶

9. Acknowledgments

TODO¶

Author's Address