J3.x:Creating an Authentication Plugin for Joomla/10/en

From Joomla! Documentation

For our example, the authentication check that we are going to do is very simple. We will simply make sure that the specified username exists in the users table, and if it does, we will check to see if the username is the reverse of the password. Note since Joomla 3.1 that the database object is created in the constructor so we can call it with $db. So our authentication check will look like: