I am using PHP and the codeigniter framework for a project I am working on, and require a user login/authentication system.

For now I'd rather not use SSL (might be overkill and the fact that I am using shared hosting discourages this). I have considered using openID but decided that since my target audience is generally not technical, it might scare users away (not to mention that it requires mirroring of login information etc.). I know that I could write a hash based authentication (such as sha1) since there is no sensitive data being passed (I'd compare the level of sensitivity to that of stackoverflow).

That being said, before making a custom solution, it would be nice to know if there are any good libraries or packages out there that you have used to provide semi-secure authentication? I am new to codeigniter, but something that integrates well with it would be preferable. Any ideas? (i'm open to criticism on my approach and open to suggestions as to why I might be crazy not to just use ssl). Thanks in advance.

Update: I've looked into some of the suggestions. I am curious to try out zend-auth since it seems well supported and well built. Does anyone have experience with using zend-auth in codeigniter (is it too bulky?) and do you have a good reference on integrating it with CI? I do not need any complex authentication schemes..just a simple login/logout/password-management authorization system.

Also, dx_auth seems interesting as well, however I am worried that it is too buggy. Has anybody else had success with this?

I realized that I would also like to manage guest users (i.e. users that do not login/register) in a similar way to stackoverflow..so any suggestions that have this functionality would be great