# File lib/fog/aws/models/iam/managed_policy.rb, line 19
        def attach(user_or_username)
          requires :arn

          username = if user_or_username.respond_to?(:identity)
                       user_or_username.identity
                     else
                       user_or_username
                     end

          service.attach_user_policy(username, self.arn)
        end