Return Errors on forms

[eluser]JoostV[/eluser]
Not sure what you mean. Validation of your forms (required|maxlength[], etc): check the form_validation library in the userguide

Wrong username/paswword combination: query the database for a user that has the existing username/password combination and grant access if they do.

Authentication is full of security issues. If you are not familiar with authentication you might be better off using one of the authentication libraries in the Wiki.