Make authentication work with 'Desktop' type Facebook application api keys.

*) Use https for getSession
*) Process the 'secret' field returned by getSession and use that for subsequent method signature generation

NB: There is still a bug in the FB server/application registration system, that causes an empty 'secret' field to be returned if the application was originally registered as being of type 'Website'.

Create a new app, fill the 'Optional' fields out accordingly, and use those keys if this affects you.