[LYB-9] OAuth2 Authentication

[rtrox]

Success Criteria:

Users can be authenticated via OAuth2. If an authenticated OAuth2 request does not resolve to an existing user, a user should be created automatically. the OAuth2 provider will be expected to handle limiting authentication to specific users if needed.

Out of Scope:

• Group / Role authorization. This will be handled in a later ticket.

_{From SyncLinear.com | LYB-9}