The site has multiple domains (and subdomains), visitors log in through a single XenForo installation which is bridged to WordPress (XenScripts) and MediaWiki (XF-MW bridge add-on).
There needs to be a single sign on, with the member being logged into the master domain on the network and as the member hits a trusted domain then they are logged in via the background (no more login login login).
I started a thread on XenScripts. See post #6 for some ideas taken from StackOverflow.
Please let me know if you are developer interested in getting this done.