I run a niche tabletop gaming site which started off with my own engine and authentication systems. I then added SMF forum systems later integrated into my website running them on the same database but with separate user tables. I achieved this through SMF because it provides both an SSI plugin system allowing you to achieve common functions for retrieving forum data in your own site and also allowing a custom function in the authentication procedure to use your own. I effectively disabled the SMF login and registration systems completely and use my own authentication checks to login the users to the forum. With this I'm able to integrate functions from my site into the forum profiles and posts as well, as the user tables are linked. I'm currently in the planning stages of a new version, a complete re-design to HTML5/CSS3 core, (hopefully) responsive design, tablet friendly etc. and I've been looking at XenForo for some time and decided I want to try and use this system for my new site version. So now that I've rambled on about my current setup, I'm wondering what XenForo has for site integration. Is there any kind of SSI for doing authentication so I could drop my own built-in system and use yours instead to link everything to the forum user accounts instead of my own. OR Do you allow a authentication function to be added to the authentication procedures in XenForo to duplicate what I'm doing now? Is there any kind of SSI for pulling information from XenForo like latest unread posts, pm notifications etc? Ultimately I'll be expanding my system beyond the single gaming site to a network of sites with subdomains but a single forum to cater for them all so a centralized authentication system is imperative.