I try to upgrade a plug-in that was on webaccess 2008. Whe were using WebAccessSession to get the user name of the current user logged (WebAccessSession.Current.Connection.UserName ). I Imagine now that it is in tfsConnection but I'm not sure.
Is there any documentation that tells what really changes between Team Foundation Server 2008 and Team Foundation Server 2010?
As far as your question about Web Access, this blog post from Hajan Eskci details what's happening with Web Access:
Team System Web Access in TFS 2010 Beta1
Until now, Team System Web Access was published as an out of band power tool. In this release and beyond, Web Access is now an integrated part of TFS, and it is installed by default when you install TFS.
No documentaion that details things at the level that you are looking for I'm afraid. As far as I know, plugging in to Web Access is not supported via any specified API so any integration you have done yourself would be classed as unsupported so you'd be on your own when it comes to figuring those sorts of changes out. Sorry.