anchor.diff:        When your app is launched from a Tool Consumer (such as Canvas),
         it will send a post request to your launch endpoint with a
         bunch of parameters. One of the received parameters in the
  -      request will be <i><strong>oauth_consumer_key</i></strong>. This
  -      key should be exactly the same as the one we defined
  +      request will be <i><strong>oauth_consumer_key</i></strong>.
  +      This key should be exactly the same as the one we defined
         in the <i><strong>settings.yml</i></strong> file.
         The first step in a request validation is to check whether this
         received key is present in your system.
  
positive.code:     </p><br>
      <p>
        <strong>Step 13:</strong>
        If you launch your application now to take an assessment, you will receive the
        following error:
        <br><br>
        <div class="text-center">
          <%= image_tag "invalid_authenticity.png", style:'width:40%' %>
        </div><br><br>
        To fix this, you need to tell Rails that it does not need to
        verify user before launch request. Add the following line in
        the <strong>application controller</strong>.<br><br>
        <pre>
          skip_before_action :verify_authenticity_token, only: :launch</pre>
      </p><br>
  
negative.code:           If the two signatures match, only then the request is valid.
          </li>
        </ol>
        Fortunately, the IMS-LTI gem will do both of these steps for us.
        It will validate the LTI request and will also perform OAuth
        authentication.
        Add the following code in the launch endpoint.
        The first part creates a Tool provider object with a key and a
  