code: public function getUserAgentHeader()
      {
          // If has own User-Agent
          $userAgentName = $this->getUserAgentName();
          if ($userAgentName) {
              return $userAgentName;
          }
  
          $userAgent = sprintf('%s/%s/%s (PHP/%s.%s.%s', $this->getLibraryName(), $this->getVersion(), $this->getPublicKey(), PHP_MAJOR_VERSION, PHP_MINOR_VERSION, PHP_RELEASE_VERSION);
  
          $framework = $this->getFramework();
          if ($framework) {
              $userAgent .= '; '.$framework;
          }
  
          $extension = $this->getExtension();
          if ($extension) {
              $userAgent .= '; '.$extension;
          }
  
          $userAgent .= ')';
  
          return $userAgent;
      }
docs: Returns full user agent string.
  
  @return string