Impossible to authenticate through OAuth Provider when `/login` without a login session

[frankie567]

Discussed in https://github.com/orgs/fief-dev/discussions/191

^{Originally posted by aido-ai May 15, 2023}
Hello, I have a new question to ask. After creating a new workspace B on the default workspace (fief), I added a new GitHub oAuth Provider.

However, when I log in through GitHub oAuth on B.ROOTDOMAIN/login (request link: https://b.rootdomain/oauth/authorize?tenant=TENANT_ID&provider=PROVIDER_ID),

I receive an "Invalid login session" error (server log: 2023-05-15 13:53:47.546 | INFO | uvicorn.protocols.http.httptools_impl:send:506 - 10.244.0.94:0 - "GET /oauth/authorize?tenant=TENANT_ID&provider=PROVIDER_ID HTTP/1.1" 400 - {}).

What usually causes this issue? I reviewed the relevant configuration again and didn't find any anomalies.

Thank you!