Allow Patrons to authenticate with existing Drupal account

Hello,

Thanks for your work on this module. One feature I think is missing is the ability for users who already have accounts on the site to link to their Patreon account. (Currently, new users can register an account, but there doesn't seem to be an option for existing users - unless I'm missing something?)

Ideally I think a button on the user edit / account page, "Authorize with Patreon" or something to that effect, which launches the Oauth method at Patreon. Users login to Patreon and then are redirected to the site and are authenticated.

It seems like this functionality already exists in the module, but the methods are contained within the module's provided login blocks which only show for anonymous users.

I can probably write a patch for this, as it seems like it might be a simple addition.