Hello! With recent enhancements in the library we may be able to greatly streamline this PR by adding a listener here (thanks to the removal of Transporter):

• google-auth-library-nodejs/src/auth/authclient.ts

  Lines 325 to 345 in a511e56

  	static readonly DEFAULT_REQUEST_INTERCEPTOR: Parameters<
  	Gaxios['interceptors']['request']['add']
  	>[0] = {
  	resolved: async config => {
  	// Set `x-goog-api-client`, if not already set
  	if (!config.headers.has('x-goog-api-client')) {
  	const nodeVersion = process.version.replace(/^v/, '');
  	config.headers.set('x-goog-api-client', `gl-node/${nodeVersion}`);
  	}
  	// Set `User-Agent`
  	const userAgent = config.headers.get('User-Agent');
  	if (!userAgent) {
  	config.headers.set('User-Agent', USER_AGENT);
  	} else if (!userAgent.includes(`${PRODUCT_NAME}/`)) {
  	config.headers.set('User-Agent', `${userAgent} ${USER_AGENT}`);
  	}
  	return config;
  	},
  	};

Every auth request goes through this function. Let me know if you’d like to sync on this or have any questions.

@d-goog Ah, lovely. Thanks!