JWT Login Type

Synapse comes with a non-standard login type to support JSON Web Tokens. In general the documentation for the login endpoint is still valid (and the mechanism works similarly to the token based login).

To log in using a JSON Web Token, clients should submit a /login request as follows:

{
  "type": "org.matrix.login.jwt",
  "token": "<jwt>"
}

The token field should include the JSON web token with the following claims:

• A claim that encodes the local part of the user ID is required. By default, the sub (subject) claim is used, or a custom claim can be set in the configuration file.
• The expiration time (exp), not before time (nbf), and issued at (iat) claims are optional, but validated if present.
• The issuer (iss) claim is optional, but required and validated if configured.
• The audience (aud) claim is optional, but required and validated if configured. Providing the audience claim when not configured will cause validation to fail.

In the case that the token is not valid, the homeserver must respond with 403 Forbidden and an error code of M_FORBIDDEN.

As with other login types, there are additional fields (e.g. device_id and initial_device_display_name) which can be included in the above request.

Preparing Synapse

The JSON Web Token integration in Synapse uses the Authlib library, which must be installed as follows:

• The relevant libraries are included in the Docker images and Debian packages provided by matrix.org so no further action is needed.

• If you installed Synapse into a virtualenv, run /path/to/env/bin/pip install synapse[jwt] to install the necessary dependencies.

• For other installation mechanisms, see the documentation provided by the maintainer.

To enable the JSON web token integration, you should then add a jwt_config option to your configuration file. See the configuration manual for some sample settings.

How to test JWT as a developer

Although JSON Web Tokens are typically generated from an external server, the example below uses a locally generated JWT.

1. Configure Synapse with JWT logins, note that this example uses a pre-shared secret and an algorithm of HS256:

   jwt_config:
       enabled: true
       secret: "my-secret-token"
       algorithm: "HS256"
   

2. Generate a JSON web token:

   You can use the following short Python snippet to generate a JWT protected by an HMAC. Take care that the secret and the algorithm given in the header match the entries from jwt_config above.

   from authlib.jose import jwt
   
   header = {"alg": "HS256"}
   payload = {"sub": "user1", "aud": ["audience"]}
   secret = "my-secret-token"
   result = jwt.encode(header, payload, secret)
   print(result.decode("ascii"))
   

3. Query for the login types and ensure org.matrix.login.jwt is there:

   curl http://localhost:8080/_matrix/client/r0/login
   

4. Login used the generated JSON web token from above:

   $ curl http://localhost:8082/_matrix/client/r0/login -X POST \
       --data '{"type":"org.matrix.login.jwt","token":"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJ0ZXN0LXVzZXIifQ.Ag71GT8v01UO3w80aqRPTeuVPBIBZkYhNTJJ-_-zQIc"}'
   {
       "access_token": "<access token>",
       "device_id": "ACBDEFGHI",
       "home_server": "localhost:8080",
       "user_id": "@test-user:localhost:8480"
   }
   

You should now be able to use the returned access token to query the client API.