Matrix Token validation between servers
The GET endpoint /_matrix/federation/v1/openid/userinfo can be used to validate an access token generated through the OpenID API and check that the user to whom the token is attached is logged in (the access token is passed as an url parameter)
This endpoint checks if the access token url parameter is stored in the "open_id_tokens" datatable.
Currently no token is stored so the /_matrix/federation/v1/openid/userinfo always returns an error indicating that the access token is not known or has expired.
We have to call the POST endpoint /_matrix/client/v3/user/{userId}/openid/request_token if we want to get and store an access token