Keycloak bearer tokens issued for thirdroom.io are enormous

My access token in an OIDC world with KC has ended up being 1743 bytes long (of base64). This is crazy long, especially given how many requests Matrix does, and especially given we finally stripped down the size of access_tokens in synapse to be something sensible in https://github.com/matrix-org/synapse/pull/5588, inspired by https://github.blog/2021-04-05-behind-githubs-new-authentication-token-formats/

No files, tests, or entry points are named in the issue. Start by locating how Keycloak issues bearer tokens for thirdroom.io and how Matrix requests consume them; done means the token size is reduced without breaking authentication.

Written by the indexing model from the issue text.