I developed this small library to handle the most simple of authentication schemes for all my Code Igniter projects. This can be expanded on but assumes you have a users table in your database with a username, and password field. The password is the md5 of the actual password.
The password hash generated is a regular md5() which is considered insecure. You can expand the operation of this authentication scheme by incoporating a salt and using a strong hashing function.