Native OIDC

[liamdiprose]

Describe the problem

Matrix is adopting OpenID Connect (OIDC) for authentication so clients will need to implement "Native OIDC".

Describe the solution you'd like

This means Cinny will need to:

• implement the single-sign-on (sso) login flow with a OIDC authorization server, and
• use the resulting access token in the Authorization header of Matrix API requests.

Alternatives considered

No response

Additional context

I have some experience implementing these flows so can provide assistance. However I think it would be best if a maintainer integrates the feature into the codebase.

There's a good overview of the process here: https://areweoidcyet.com/client-implementation-guide/

[kfiven]

https://synapse-oidc.element.dev as a server seems to work already or is there something else more needed to implement Native OIDC?

[liamdiprose]

Hi @kfiven,

I've opted into MSC3861 which changes synapse's auth system to OIDC in my homeserver.yaml:

experimental_features:
  msc3861:
    enabled: true
    client_id: _oidc_client_id_
    client_secret: _oidc_client_secret_
    issuer: https://_oidc_hostname_

Now synapse responds to /login/* requests with 404.

To help migration, the Matrix maintainers have released the matrix-authentication-service (MAS) to translate the issuer into the old /login response (1). I guess this is what https://synapse-oidc.element.dev is doing.

The matrix maintainers stated in the Matrix 2 announcement that they plan to decommission MAS on matrix.org soon. Given the choice, I'd much rather add native OIDC behaviour to Cinny than get MAS working.

At the moment, Cinny only requests the /login route and I don't see the request to discover the OIDC issuer:

GET https://synapse-oidc.element.dev/_matrix/client/unstable/org.matrix.msc2965/auth_issuer

Using that response, Cinny needs to construct it's own OIDC redirect URL and handle when the OIDC server redirects the user's browser back to Cinny. The redirect URL will contain a code which Cinny can then exchange with the OIDC server for an access token.

I'm happy to help if you have any questions with regards to the OIDC redirect login flow.