Luckily, Moodle supports a range of different authentication protocols out of the box, each one supported by its own plugin. We should say at the outset that this means that it is unlikely to be necessary for you to create a new plugin. So, before you do decide to create a new authentication plugin, it is best to make absolutely certain that your authentication requirements can't already be accommodated. To go to the list of available plugins, from the Administration block, click on Site administration, click Plugins, then click Authentication, and finally click on Manage authentication. The list of currently installed authentication plugins is displayed:
Each plugin interfaces with the Access API--see the Moodle developer documentation for details at: https://docs.moodle.org/dev/Access_API.