If you use ASP.NET (webforms or MVC) you may want to use MySQL as your database.  One nice feature of .NET is the Membership Provider which takes care of authentication and authorization.  You can use MySQL to store the necessary informaion for the membership and role providers.  The below article details how to do this:

 

http://dev.mysql.com/doc/refman/5.1/en/connector-net-tutorials-asp-roles.html 

 

If you run into issues, make sure you copy the MySQLMembershipProvider and MySQLProfileProvider sections from the machine.config to your local web.config.  Once you do this, you should be all set.