Here is the function, drop it in your functions.php file:
function auto_login( $user ) { $username = $user; if ( !is_user_logged_in() ) { $user = get_userdatabylogin( $username ); $user_id = $user->ID; wp_set_current_user( $user_id, $user_login ); wp_set_auth_cookie( $user_id ); do_action( 'wp_login', $user_login ); } }
Then, to log in a user, do the following:
auto_login( 'admin' )
Thanks evilsocket for the code!