This implements a fake OIDC server, which intercepts calls to the HTTP client.
Improves accuracy of tests by covering more internal methods.
One particular example was the ID token validation, which previously mocked.
This uncovered an incorrect dependency: Synapse actually requires at least
authlib 0.15.1, not 0.14.0.
When configuring the return values of mocks, prefer awaitables from
`make_awaitable` over `defer.succeed`. `Deferred`s are only awaitable
once, so it is inappropriate for a mock to return the same `Deferred`
multiple times.
Also update `run_in_background` to support functions that return
arbitrary awaitables.
Signed-off-by: Sean Quah <seanq@element.io>
This is an endpoint that we have server-side support for, but no client-side support. It's going to be useful for resyncing partial-stated rooms, so let's introduce it.