create remote evaluation

app/models/remote_evaluation_mapping.rb

@@ -0,0 +1,10 @@
+# todo: reference to lti_param_model
+class RemoteEvaluationMapping < ActiveRecord::Base
+  before_create :generate_token, unless: :validation_token?
+  belongs_to :exercise
+  belongs_to :user
+
+  def generate_token
+    self.validation_token = SecureRandom.urlsafe_base64
+  end
+end