Extract shared sign-in shim logic

This makes it easier in the future to provide the `sign_out` parity when
we want include the `sign_in` helper. We name the module as a "shim" to
help indicate the behavior of the module; i.e. shimming in some logic,
instead of changing a configuration, intercepting remote auth calls,
etc.

Author: cupakromer

lib/kracken/rspec.rb

@@ -12,14 +12,18 @@ def self.current_user=(current_user)
       @@current_user = current_user
     end
 
-    module Request
+    module SignInShim
       def sign_in(user = nil)
         Kracken::SpecHelper.current_user = user
       end
 
       def sign_out(_ignored = nil)
         Kracken::SpecHelper.current_user = nil
       end
+    end
+
+    module Request
+      include SignInShim
 
       def token_authorize(user, token:)
         Kracken::Controllers::TokenAuthenticatable::cache_valid_auth(token, force: true) do
@@ -29,21 +33,13 @@ def token_authorize(user, token:)
     end
 
     module Controller
-      def sign_in(user = nil)
-        Kracken::SpecHelper.current_user = user
-      end
-
-      def sign_out(_ignored = nil)
-        Kracken::SpecHelper.current_user = nil
-      end
+      include SignInShim
 
       def current_user
         Kracken::SpecHelper.current_user
       end
     end
-
   end
-
 end
 
 # monkey patch current_user