title: Fail2Ban how to match any string
body: <p>I have a very simple situation but I can't figure out how regex works...
  I have an application generating a log only when a login problem occurs. So there is no line in log except in case of wrong login or in case of attempt to reset a password too many times. So potentially, I don't even need to search a particular string in log, any entry matches. Here is a log example :</p>
  
  <pre><code>2019-10-20 18:44:35 127.0.0.1 login.php : Authentication error - account not initialized : client XXXX, login YYYY
  2019-10-20 21:31:17 127.0.0.1 login.php : Authentication error - password error : client XXXX, login XXXX
  2019-10-20 21:29:39 127.0.0.1 login.php : Authentication error - client contains wrong chars : client XXXX, login YYYY 
  2019-10-21 06:25:25 127.0.0.1 login.php : Authentication error - account locked : client XXXX, login YYYY
  2019-10-21 06:48:11 127.0.0.1 user.php : Authentication - Unlocking : client XXXX, login YYYYY
  </code></pre>
  
  <p>I have a problem with regular expression cause I can't understand how it works (for years). All I tried give me errors when I start fail2ban : Unable to compile regular expression,  No failure-id group in 'Authentication error', ... Damned, it looks so easy !</p>