Case insensitive login class

[eluser]Kurai[/eluser]
Hi there!
I'm building my own login class inside my application. I used Simple login just to learn the mechaniscs and the basic structure, and I have two questions.

First one: is really ok to have all the check routines (which of course involve the database) in a library? Shouldn't be better to use a model instead?

Second one: simplepie checks if the username exists in the database this way:

Code:

$this->CI->db->where('username', $user);
$query = $this->CI->db->getwhere($this->user_table);

Which is obviously good if you want a case-sensitive login. What if I'd like to have username put into the database as is, but case-insensitive control? Thank you!