Drops the dedicated /settings/authentication/providers/{provider}/callback
route added in the previous refactor — registering a second callback URL
in each OAuth app is more ops cost than the trade is worth.
Back to one callback URL per provider, with a small `Auth::check()`
branch in the auth controllers' callbacks. The check is safe because
the redirects that initiate the round-trip enforce the right
middleware (signup/login is `guest`-only, connect is `auth`-only),
so the auth state at callback time matches the flow's intent.
Splits the OAuth connect flow off entirely from signup/login so each
route has a single responsibility.
- routes/auth.php returns to its original state — redirect + callback
both back inside the `guest` group.
- routes/app.php gains a paired callback route at
/settings/authentication/providers/{provider}/callback.
- AuthenticationController::connectProvider /
connectProviderCallback override Socialite's redirectUrl so the
round-trip stays on the connect-flow URL. The Auth::check() branch
in the auth controllers is gone.
The OAuth apps in Google Cloud and GitHub Developer Settings need the
new callback URL registered alongside the existing one — documented in
.env.example.
The Connect button on /settings/authentication pointed at the
auth.{provider}.redirect routes that live behind `guest` middleware,
so authenticated users were bounced to /app/home before reaching
Socialite. The OAuth callback also needed to handle two flows
(signup/login vs link to current user) but had no branch for the
second case — meaning a different-email GitHub account would have
been registered as a new user, logging the original session out.
Splits the flows by intent:
- New `app.authentication.connect-provider` route in the auth group,
handled by the settings controller (where it sits next to
disconnect-provider). Replaces the OAuth signup link as the
Connect button's target.
- Auth callbacks moved out of the guest group (still one URL per
provider, since OAuth apps only register one) and gain a single
Auth::check() branch that calls connectToCurrentUser().
- connectToCurrentUser() rejects if the provider id already belongs
to a different user; otherwise sets it on the current user and
redirects back to settings with a flash message.
