Nested JSON Web Token (JWT)
draft-yusef-oauth-nested-jwt-02

Abstract

This specification extends the scope of the Nested JSON Web Token (JWT) to allow the enclosing JWT to contain its own Claims Set in addition to the enclosed JWT.

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Table of Contents

• 1. Introduction
• 1.1. Terminology
• 2. Overview
• 3. Use Cases
• 3.1. Native App
• 3.2. STIR
• 4. JWT Content Type Header Parameter
• 5. JWT Content
• 6. Example
• 7. Security Considerations
• 8. IANA Considerations
• 9. Acknowledgments
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Author's Address

1. Introduction

JSON Web Token (JWT) 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.

This specification extends the scope of the Nested JWT to allow the enclosing JWT to contain its own Claims Set in addition to the enclosed JWT.

1.1. Terminology

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 [RFC8174].

2. Overview

RFC7519 defines Nested JWT as a JWT in which nested signing and/or encryption are employed. In Nested JWTs, a JWT is used as the payload or plaintext value of an enclosing JWS or JWE structure, respectively.

To indicate that the payload of an enclosing JWT is yet another JWT, the value of the Content Type Parameter of the JOSE header, i.e. "cty", must be set to "JWT", which means that the enclosing JWT cannot have its own claims.

This document updates the enclosing JWT content to allow it to represent a Claims Set and an enclosed JWT, using JSON data structures, and updates the Content Type to indicate this new nested content.

3. Use Cases

3.1. Native App

The use case is for a telephony application that is based on the "Native Apps Using the Browser" flow defined in RFC8252. The Native App needs access to a telephony and non-telephony services that are controlled by different authorization servers, where the Native App can validate tokens issued by only one of these authorization servers.

The Native App starts the process by interacting with a Client that requires the user to authenticate itself using a Browser. The Browser starts by contacting an AS, which redirects it to an OP. The user authenticates to the OP and obtains a Code, and then gets redirected back to AS. The Native App gets access to the Code, then sends the Code to the AS, which then interacts with the OP to exchange the Code for an ID Token and OP Access Token. Since the Native App has no way of validating the OP Access Token, when the AS creates an AS Access Token, it embeds the OP Access Token inside the AS Access Token, and returns it back to the Native App. The Native App gets the AS Access Token and is able to validate it and extract the OP Access Token, and access the different services protected with these tokens.

3.2. STIR

[RFC8225] defines a PASSporT, which is a JWT, that is used to verify the identity of a caller in an incoming call.

The PASSporT Extension for Diverted Calls draft [STIR] uses a nested PASSporT to deliver the details of an incoming call that get redirected. An authentication service acting for a retargeting entity generates new PASSporT and embeds the original PASSporT inside the new one. When the new target receives the nested PASSporT it will be able to validate the enclosing PASSporT and use the details of the enclosed PASSporT to identify the origianl target.

4. JWT Content Type Header Parameter

The JOSE Header contains an optional parameter that could be used to indicate the type of the payload of a JWT. With a typical Nested JWT, the value of the "cty" header must be "JWT". To indicate that the payload contains a Claims Set in addition to the JWT, the value of the "cty" header must be "NJWT".

5. JWT Content

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

This document defines a new claim, "njwt", that is used to contain the enclosed JWT.

6. Example

{
  "alg": "HS256",
  "typ": "JWT",
  "cty": "NJWT"
}

{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022,
  "njwt": "<njwt>"
}

7. Security Considerations

TODO

8. IANA Considerations

TODO

9. Acknowledgments

TODO

10. References

10.1. Normative References

10.2. Informative References

Author's Address