Add reset_session for the :reset_session strategy.

lib/omni_auth/request_forgery_protection.rb

 # Protects OmniAuth request phase against CSRF.
 
 module OmniAuth
-  # Based from ActionController::RequestForgeryProtection.
+  # Based on ActionController::RequestForgeryProtection.
   class RequestForgeryProtection
     def initialize(env)
       @env = env
@@ -15,6 +15,10 @@ module OmniAuth
       request.session
     end
 
+    def reset_session
+      request.reset_session
+    end
+
     def params
       request.params
     end