When a user signs up via an external auth method, a new link is added to the signup modal which allows them to connect an existing Discourse account. This will only happen if:
- There is at least 1 other auth method available
and
- The current auth method permits users to disconnect/reconnect their accounts themselves
This handles a few edge cases which are extremely rare (due to the UI layout), but still technically possible:
- Ensure users are authenticated before attempting association.
- Add a message and logic for when a user already has an association for a given auth provider.
Plugins listening on the `before_auth` callback can interact with the request object and access data like the user agent or the remote IP address. We'll later store this data in the user record, but it might not exist at this point if we're authenticating a new account.
