Moodle is a free and open-source software learning management system written in PHP and distributed under the GNU General Public License. Moodle is used for blended learning, distance education, flipped classroom and other e-learning projects in schools, universities, workplaces and other sectors.

Our main objective is that we wanted to manage all the users from Drupal i.e., use drupal as the front end for managing users. For this purpose, we have a moodle plugin and drupal module. Drupal services is a moodle authorization plugin that allows for SSO between Drupal and Moodle. Moodle SSO provides the Drupal functionality required to allow the Moodle training management system to SSO share Drupal sessions. 

In order to make SSO work, we need to ensure that sites can share cookies. Drupal and moodle sites should have url like drupal.example.com and moodle.example.com. As mentioned earlier, sites should be able to share cookies. To make sites use shared cookie, we need set the value of $cookie_domain in settings.php file on the drupal site. In our case, the site urls was something like drupal.example.com and moodle.example.com. For these type of sub-domains, the cookie_domain value can be set like the below one:

$cookie_domain = ".example.com";

Note: The dot before "example.com" is necessary.

Let's start with the steps that need to followed for achieving SSO between drupal and moodle:

1. Moodle site