add current_user_provider so people can override current_user bevior cleanly, see

http://meta.discourse.org/t/amending-current-user-logic-in-discourse/10278

lib/auth/current_user_provider.rb

@@ -0,0 +1,34 @@
+module Auth; end
+class Auth::CurrentUserProvider
+
+  # do all current user initialization here
+  def initialize(env)
+    raise NotImplementedError
+  end
+
+  # our current user, return nil if none is found
+  def current_user
+    raise NotImplementedError
+  end
+
+  # log on a user and set cookies and session etc.
+  def log_on_user(user,session,cookies)
+    raise NotImplementedError
+  end
+
+  # api has special rights return true if api was detected
+  def is_api?
+    raise NotImplementedError
+  end
+
+  # we may need to know very early on in the middleware if an auth token
+  # exists, to optimise caching
+  def has_auth_cookie?
+    raise NotImplementedError
+  end
+
+
+  def log_off_user(session, cookies)
+    raise NotImplementedError
+  end
+end