code: func FetchGoogleOAuth2Certificates(c context.Context) (*PublicCertificates, error) {
  	certs, err := certsCache.LRU(c).GetOrCreate(c, "google_auth2_certs", func() (interface{}, time.Duration, error) {
  		certs, err := fetchCertsJSON(c, oauth2CertsURL)
  		if err != nil {
  			return nil, 0, err
  		}
  		return certs, CertsCacheExpiration, nil
  	})
  	if err != nil {
  		return nil, err
  	}
  	return certs.(*PublicCertificates), nil
  }
docs: // FetchGoogleOAuth2Certificates fetches root certificates of Google OAuth2
  // service.
  //
  // They can be used to verify signatures on various JWTs issued by Google
  // OAuth2 backends (like OpenID identity tokens and GCE signed metadata JWTs).
  //
  // Uses the process cache to cache them for CertsCacheExpiration minutes.