This is what the username_hooks are for. See the comments in config/hooks.php.

We were having problems with sub applications like Turba and Nag when 
a user authenticated with uppercase characters in their username. We 
are using Imp with Imap for authentication, and so this works, but 
when a user submitted data in an application like Turba, the owner in 
the database table (ie. turba_objects and owner_id) would contain the 
uppercase characters. This prevented them from viewing the data if 
they later logged in with all lowercase, or any other combination of 
upper and lowercase characters in their username, which differed from 
what they used when they entered the data.



To fix this problem, I modified horde's Auth::getAuth() method adding 
a check for the configuration variable 
$GLOBALS['conf']['auth']['lowercase'], and if that was set, to run the 
return result through strtolower(). This seems to have fixed all the 
problems.



I have included my patch, and believe it would be a nice option added 
for any other imp and imap authentication users.



Run patch from the horde install directory with -p0