Redirect or do something if the authentication fails

[Mica-CRT]

Hi!, i tried to install this repo on my setup and works very well; but i noticed that if the authentication fails (such as incorrect passwd/user or an inexistent account) the page cause a 500 internal error, how can i do a possible redirect to the eventual log-in page or a personalized log-in error page?
I tried to check if some connection's/authentication's method return a "false" value or something like this and do some conditions but the browser still show me a 500 internal error.