InstaLogin is a Safari App Extension that allows you to automatically login in websites instantly with Safari AutoFill!
How it works in three steps:
1. Use AutoFill or type your user and password in a login page.
2. Click the Bolt button in the Safari toolbar (save your credentials in Safari AutoFill if asked).
3. Now InstaLogin will auto-login you in that site every time it detects that your credentials are filled by AutoFill in the login form. Instantly!
Suggestions are welcomed at @pvieito.