mongodb - How to use Devise authorization in custom middleware -

i have middleware serving files mongodb

#serve_gridfs_file.rb class servegridfsfile   def initialize(app)     @app = app   end    def call(env)     if env["path_info"] =~ /^\/grid\/(.+)$/       process_request(env, $1.force_encoding("utf-8"))     else       @app.call(env)     end   end    private     def process_request(env, key)     begin       mongo::gridfilesystem.new(mongoid.database).open(key, 'r') |file|         [200, { 'content-type' => file.content_type }, [file.read]]       end     rescue      [404, { 'content-type' => 'text/plain' }, ['file not found.']]     end   end end 

i use devise capabilities current_user. after that, use validation. not know how in simple manner.