event_log_track_auth does not track all user login events

Problem/Motivation

Login methods that bypass the user login form are not tracked by the event log. Examples:

• When using a one-time login link.
• When using the External Authentication module to integrate with a third-party single sign-on solution.
• When using the Masquerade module to masquerade as another user.

Steps to reproduce

1. Use drush uli to generate a one-time login link.
2. Click the link.
3. Go to /admin/reports/events-track.

Expected result: There is a login event in the log.
Actual result: No login event is logged.

Proposed resolution

The problem occurs because event_log_track_auth is hooking into the user_login_form to detect logins. If it instead used hook_user_login(), it should work for both standard logins through the form and for the exceptional cases noted above.