fixes #2478: Add links for easy opt-out of emails

app/controllers/maintenance/user/email_notifications_controller.rb

@@ -0,0 +1,33 @@
+module Maintenance
+  module User
+    class EmailNotificationsController < ApplicationController
+      class VerificationError < Exception ; end
+
+      before_filter :validate_sig, :only => [:destroy]
+      rescue_from VerificationError, :with => :render_403
+
+      def show
+      end
+
+      def destroy
+        @user = User.find(params[:user_id])
+        @user.receive_email_notifications = false
+        @user.save
+      end
+
+    private
+
+      def render_403
+        render :nothing => true, :status => 403
+      end
+
+      def validate_sig
+        digest = OpenSSL::Digest.new("sha256")
+        calc_sig = OpenSSL::HMAC.hexdigest(digest, Danbooru.config.email_key, params[:user_id].to_s)
+        if calc_sig != params[:sig]
+          raise VerificationError.new
+        end
+      end
+    end
+  end
+end