code: private function setAuthorizationHeader(string $accessToken): self
      {
          $this->accessToken = $accessToken;
  
          $this->options->set(
              'default_headers',
              array_merge(
                  $this->options->get('default_headers'),
                  [
                      'Authorization' => 'Bearer ' . $accessToken,
                  ]
              )
          );
  
          return $this;
      }
docs: set header for OAuth 2.0