Here is a workaround the missing Session problem:

On the webpage before you like to automatic login to the chat, you need to add the nick to the HttpContext.Items collection. Because the context is ok, it is the context.Session, that is the problem. In your custom implementation of the UserAdapter, you need to check if the context.Session==null, if it is, then use the context.Items collection to retrieve the nick.

 
Still hoping to here about the resize of the chat?

Brgds