preparations to replace session with lti_parameters object

db/migrate/20161214144837_create_lti_parameters.rb

@@ -0,0 +1,12 @@
+class CreateLtiParameters < ActiveRecord::Migration
+  def change
+    create_table :lti_parameters do |t|
+      t.string :external_user_id
+      t.belongs_to :consumers
+      t.belongs_to :exercises
+      t.column :lti_parameters, :jsonb
+
+      t.timestamps
+    end
+  end
+end