code: public function authenticate($username, $password)
      {
          if (! $this->page->getRealm()) {
              return false;
          }
          $url = $this->page->getUrl();
          if (! $url) {
              return false;
          }
          $this->user_agent->setIdentity(
                  $url->getHost(),
                  $this->page->getRealm(),
                  $username,
                  $password);
  
          return $this->retry();
      }
docs: Retries a request after setting the authentication for the current realm.
  
  @param string $username    Username for realm.
  @param string $password    Password for realm.
  
  @return bool    True if successful fetch. Note that authentication may still have failed.