code: public function requestKeyValueForm(string $method, string $uri, ?array $get = null, ?array $post = null, ?array $files = null, ?array $headers = null): array
      {
          $options = $this->prepareOptions($get, $post, $files, $headers);
          $response = $this->request($method, $uri, $options);
          if (!preg_match_all("#(?<key>.+?)\:(?<value>.+)#", (string) $response->getBody(), $matches)) {
              throw new ParseContentException($response, 'key-value');
          }
  
          return array_combine($matches['key'], $matches['value']);
      }
docs: @see http://openid.net/specs/openid-authentication-2_0.html#anchor4
  
  @param string     $method
  @param string     $uri
  @param array|null $get
  @param array|null $post
  @param array|null $files
  @param array|null $headers
  
  @throws GuzzleException
  @throws ParseContentException
  
  @return array