chainjwt

chainjwt is a Go library for validating a JWT based on a trust assertion from another JWT.

This structure allows for:

• Private Key storage on clients in enclaves or other secure methods.
• Validation by a Services with limited need for remote queries.
• Eliminating long lived bearer tokens, since a client can mint a new request signed JWT for each request.

RFC 7517 provides the x5c and x5t parameters, which could be used for a similiar purpose using X.509 Certificate Authorities. chainjwt avoids the surface area of X.509 certificate chain verification by using a single-length chain of JWTs as the assertion method.

chainjwt depends upon Square's go-jose.v2 and ScaleFT's xjwt libraries for the heavy lifting of parsing and validating JWTs.

Details

The JWT to be verified is called the 'outer JWT'.

chainjwt adds a jwc field to the header of the outer JWT. The jwc header field contains a compact-form JWT (the 'inner JWT') that is trusted by the verifying party (similar to an X.509 Certificate Authority).

To validate a JWT, the jwc header field is first extracted, parsed, and verified from the outer JWT's header. The tjwk claim in the inner JWT is a JWK Public Key that the verifing code uses to validate the whole outer JWT. The tjwk claim could be thought of as a client certificate in an X.509 system.

The signature on the outer JWT is evidence of ownership of the associated private key referenced by the public key in the tjwk claim.

Example JWC Header

In the header of the 'outer JWT':

{
  "alg": "EdDSA",
  "jwc": "eyJhbGciOiJFZERTQSIsImtpZCI6IkUyOUE4OTlDIiwibm9uY2UiOiI2M2E1MzYzMjI3NDYwYjVhIn0.eyJhdWQiOlsiYXBpLmV4YW1wbGUuY29tIl0sImV4cCI6MTUyNjMzMjczOSwiaWF0IjoxNTI2MzMyNzA5LCJpc3MiOiJhcGkuZXhhbXBsZS5jb20iLCJqdGkiOiIwM0VDNUVGNCIsIm5iZiI6MTUyNjMzMjY3OSwic3ViIjoiQ2xpZW50IFgiLCJ0andrIjp7ImFsZyI6IkVkRFNBIiwiY3J2IjoiRWQyNTUxOSIsImtpZCI6IkJFNjBERkM4LUsxIiwia3R5IjoiT0tQIiwieCI6IjVfVm9MbjhsY3R2djJ3RVhjdlNuREVGX0JPcDhycWlVbVFmM0dwdXJUcjAifX0.OYQZRUACGE9oc-kgcBLqL5DRaTvEh3QNChBN2zrXlnDthw0PJFD7quurjDM3HaEFKC2-Uot7K0nOq2ijYo73Cg",
  "kid": "BE60DFC8-K1",
  "nonce": "77f446e8d079cb20"
}

The jwc header field contains another compact-form JWT: 👁 jwt.io

Example JWC (decoded claims)

Extracted from the jwc header in the 'outer JWT', the claims of the 'inner JWT' contain the tjwk claim:

{
  "aud": [
    "api.example.com"
  ],
  "exp": 1526332739,
  "iat": 1526332709,
  "iss": "api.example.com",
  "jti": "03EC5EF4",
  "nbf": 1526332679,
  "sub": "Client X",
  "tjwk": {
    "alg": "EdDSA",
    "crv": "Ed25519",
    "kid": "BE60DFC8-K1",
    "kty": "OKP",
    "x": "5_VoLn8lctvv2wEXcvSnDEF_BOp8rqiUmQf3GpurTr0"
  }
}

Full Bytes of an example chained JWT

👁 jwt.io

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.eyJhdWQiOlsiYXBpLmV4YW1wbGUuY29tIl0sImV4cCI6MTUyNjMzMjczOSwiaWF0IjoxNTI2MzMyNzA5LCJpc3MiOiJCRTYwREZDOCIsIm5iZiI6MTUyNjMzMjY3OSwic3ViIjoiQkU2MERGQzgifQ.ZZTFoqyc8rJmiIWfQX7IScnFUWn10JYG5T_M9rPcxivw-VBGqfGejwTvf0bAubCjlXJkeFoug4-SVlhGpc9jAA

JOSE Extensions

JOSE Headers are in assigned in an IANA registery. chainjwt adds one header type. JWT Claims are also in an IANA registry and chainjwt adds one claim type.

JSON Web Signature and Encryption Header Parameters

• jwc: JWT Chain. Contains string with a compact form JWT. This JWT is intended to be longer lived, and to be signed by a trusted JWK. This JWT contains an tjwk claim, which contains a JSON Web Key which can be used to validate the outer JWT.

JSON Web Token Claims

• tjwk: Trusted JWK. Contains a JSON-form JSON Web Key. This MUST be a public key and the verifier should restrict the allowed algorithms. This JWK can be used the validate the outer JWT.

License

chainjwt is licensed under the Apache License Version 2.0. See the LICENSE file for details.