Handles the OAuth redirect callback: validates state, surfaces error
responses, exchanges the authorization code for tokens, persists them, and
transitions to LOGGED_IN.
Returns the callback URL cleaned of OAuth params (for the caller to
history.replaceState) when a callback was processed, or false when there
was nothing to handle (no code, or an exchange already in progress).
Handles the OAuth redirect callback: validates
state, surfaceserrorresponses, exchanges the authorizationcodefor tokens, persists them, and transitions toLOGGED_IN.Returns the callback URL cleaned of OAuth params (for the caller to
history.replaceState) when a callback was processed, orfalsewhen there was nothing to handle (no code, or an exchange already in progress).