In the TutsPlus.com site there's a tutorial posted showing you how to create a custom guard in Laravel by building on top of the current system to integrate it with a MongoDB database.

In this article, we’re going to cover the authentication system in the Laravel framework. The main aim of this article is to create a custom authentication guard by extending the core authentication system.

Laravel provides a very solid authentication system in the core that makes the implementation of basic authentication a breeze. [...] Moreover, the system itself is designed in such a way that you could extend it and plug in your custom authentication adapters as well. That’s what we'll discuss in detail throughout this article.

The article then starts out with a brief description of the two parts of the system: "guards" and "providers". It then provides the list of files that will be involved and where they belong in the overall structure. From there it's on to the configuration changes and code required to make the link to the MongoDB database and the creation of the User model and authentication provider. Next comes the code to create the guard and what's required to tie it all together and make the full system work. The tutorial wraps up with an example of testing this new guard via a simple controller call.