Unlink and login link are the same so user can get unregistered on login

[vwbusguy]

I noticed that the login link and the link to unlink an OIDC are the same (/oauth/gitea in this case), so it seems that when the login is linked to from elsewhere that it is treated as an unlink instead of a login.

I setup OIDC auth through Forgejo and added a Gist link the the navbar. To make things easier on users who are already logged into forgejo to not have to click a button to login to opengist, I tried to set the link to the login like https://opengist-url/oauth/gitea, but it is redirecting to the settings page with a message that the Gitea account has been unlinked. This is a benign message, since OIDC is the only login method, but also not the expected landing page, so for now I've reverted to users having to click the login button to access gists when coming from the git forge.

This could be fixed by either only triggering the unlink when the referrer is the settings page or (probably better) changing the unlink endpoint to be distinct from the login endpoint.

[vwbusguy]

Many thanks!