Redirect velruse logins back to the page where login was performed

After logging in with Facebook(velruse), the user is redirected to URL defined by the came_from GET parameter.
Velruse can not redirect to custom URIs when used as a service and can then only be used with POST,
so adhocracy first remembers the users current URI, redirects her to a page where a login form is automatically send and then the redirect wanted performed.