Joomla manual login with controller

I am developing a component for Joomla. It has integrations with popular social websites. I retrieve user information from database via given social profile. Then, I try to make this user login with the following code:

$fbuser = $facebook->api(
                '/me',
                'GET',
                array(
                    'access_token' => $_SESSION['active']['access_token']
                )
            );

            // Get a database object
            $db =& JFactory::getDBO();
            $query = "SELECT * FROM #__users WHERE email = '".$fbuser['email']."';";
            $db->setQuery($query);
            $row = $db->loadRow();

            if(isset($row))
            {
                $app = JFactory::getApplication();
                $user =& JUser::getInstance($row[0]);

                $credentials = array();
                $credentials['username'] = $user->get('username');
                $credentials['password'] = $user->get('password'); // When I change this to related users plain password then it works

            $options = array();
                $options['remember']     = true;
                $options['silent']     = true;

                $app->login($credentials, $options);
            }
            else
            {
                return 'There is no account associated with facebook';
            }

The problem is database return encoded password and this doesn't work. When I give decoded password to $credentials it works. What can be the problem?

One option is to create your own authentication plugin (quite simple task) that would log in any user with a specific password known only to you and the site.

Then you can supply that password along with known username.

For the sake of security, only allow that plugin to log in ordinary users, and not admins.