Add nonce mismatch error workaround from Discourse

Fixes nhosoya#76

Author: quadule

lib/omniauth/strategies/apple.rb

@@ -46,6 +46,21 @@ def callback_url
         options[:redirect_uri] || (full_host + script_name + callback_path)
       end
 
+      # from https://github.com/discourse/discourse-apple-auth/blob/486ce761aa44ba9b56056963b693644efc07a72f/lib/omniauth_apple.rb#L60
+      def callback_phase
+        if request.request_method.downcase.to_sym == :post
+          url = callback_url.dup
+          if (code = request.params['code']) && (state = request.params['state'])
+            url += "?code=#{CGI::escape(code)}"
+            url += "&state=#{CGI::escape(state)}"
+            url += "&user=#{CGI::escape(request.params['user'])}" if request.params['user']
+          end
+          session.options[:drop] = true # Do not set a session cookie on this response
+          return redirect url
+        end
+        super
+      end
+
       private
 
       def new_nonce