Sign out users with wrong CSRF tokens

See http://guides.rubyonrails.org/security.html#cross-site-request-forgery-csrf

app/controllers/application_controller.rb

@@ -5,7 +5,13 @@
 class ApplicationController < ActionController::Base
   before_action :force_tablet_html
   has_mobile_fu
-  protect_from_forgery except: :receive
+  protect_from_forgery except: :receive, with: :exception
+
+  rescue_from ActionController::InvalidAuthenticityToken do
+    sign_out current_user
+    flash[:error] = I18n.t("error_messages.csrf_token_fail")
+    redirect_to new_user_session_path format: request[:format]
+  end
 
   before_action :ensure_http_referer_is_set
   before_action :set_locale

config/locales/diaspora/en.yml

@@ -75,6 +75,7 @@ en:
     helper:
       correct_the_following_errors_and_try_again: "Correct the following errors and try again."
     need_javascript: "This website requires JavaScript to function properly. If you disabled JavaScript, please enable it and refresh this page."
+    csrf_token_fail: "The CSRF token is invalid. Please sign in and try again."
 
   admins:
     admin_bar:

spec/integration/application_spec.rb

@@ -0,0 +1,48 @@
+require "spec_helper"
+
+describe ApplicationController, type: :request do
+  describe "csrf token validation" do
+    context "without a current user" do
+      before do
+        @user = alice
+        @user.password = "evankorth"
+        @user.password_confirmation = "evankorth"
+        @user.save
+      end
+
+      it "redirects to the new session page on validation fails" do
+        expect_any_instance_of(SessionsController).to receive(:verified_request?).and_return(false)
+        post "/users/sign_in", user: {remember_me: 0, username: @user.username, password: "evankorth"}
+        expect(response).to redirect_to new_user_session_path
+        expect(flash[:error]).to eq(I18n.t("error_messages.csrf_token_fail"))
+      end
+
+      it "doesn't redirect to the new session page if the validation succeeded" do
+        expect_any_instance_of(SessionsController).to receive(:verified_request?).and_return(true)
+        post "/users/sign_in", user: {remember_me: 0, username: @user.username, password: "evankorth"}
+        expect(response).to redirect_to stream_path
+        expect(flash[:error]).to be_blank
+      end
+    end
+
+    context "with a current user" do
+      before do
+        sign_in alice
+      end
+
+      it "signs out users if a wrong token was given" do
+        expect_any_instance_of(UsersController).to receive(:verified_request?).and_return(false)
+        put edit_user_path, user: {language: "en"}
+        expect(response).to redirect_to new_user_session_path
+        expect(flash[:error]).to eq(I18n.t("error_messages.csrf_token_fail"))
+      end
+
+      it "doesn't sign out users if the token was correct" do
+        expect_any_instance_of(UsersController).to receive(:verified_request?).and_return(true)
+        put edit_user_path, user: {language: "en"}
+        expect(response).not_to be_redirect
+        expect(flash[:error]).to be_blank
+      end
+    end
+  end
+end