code: def verify_request(self):
          
          if flask_request.method == 'POST':
              params = flask_request.form.to_dict()
          else:
              params = flask_request.args.to_dict()
          log.debug(params)
          log.debug('verify_request?')
          try:
              verify_request_common(self._consumers(), flask_request.url,
                                    flask_request.method, flask_request.headers,
                                    params)
              log.debug('verify_request success')
  
              # All good to go, store all of the LTI params into a
              # session dict for use in views
              for prop in LTI_PROPERTY_LIST:
                  if params.get(prop, None):
                      log.debug("params %s=%s", prop, params.get(prop, None))
                      session[prop] = params[prop]
  
              # Set logged in session key
              session[LTI_SESSION_KEY] = True
              return True
          except LTIException:
              log.debug('verify_request failed')
              for prop in LTI_PROPERTY_LIST:
                  if session.get(prop, None):
                      del session[prop]
  
              session[LTI_SESSION_KEY] = False
              raise
docs: Verify LTI request
          :raises: LTIException is request validation failed