Luciano Mammino has a quick post to his site with information that tries to help make Symfony authentication simple (well, maybe).

The Symfony2 security component has the fame of being one of the most complex in the framework. I tend to believe that's partially true, not because the component is really that complex, but because there are (really) a lot of concepts involved and it may be difficult to understand them all at once and have a clear vision as a whole.

[...] Going back to the Symfony2 security component, the point is that I found out difficult at first glance to get a clear idea of what is going on behind the scenes and what I need to write to create a custom authentication mechanism. So in this post I will try to collect few interesting resources that helped me understanding it better and a graph I drawn to resume what I learned.

He provides a good list to some of the other resources that helped him along the way including several blog posts and links to the Symfony "cookbooks" about creating custom providers. He also shares a graph showing the full flow of the Symfony authentication process including commentary about each step.