code: def prepare(self):
          
          requested_access = self.endpoint_access(self.request.method)
          use_oauth = getattr(options, 'use_oauth', None)
          if use_oauth and requested_access is not self.UNAUTHENTICATED_ACCESS:
              token = self.request.headers.get('Authorization', '').split(' ')[-1]
              if token:
                  has_access = yield self.verify_token(token, requested_access)
                  if not has_access:
                      msg = "'{}' access not granted.".format(requested_access)
                      raise HTTPError(403, msg)
              else:
                  msg = 'OAuth token not provided'
                  raise HTTPError(401, msg)
docs: If OAuth verification is required, validate provided token
  
          :raise: HTTPError if token does not have access