code: func (p *userAuthTokenProvider) grabEmail(ctx context.Context, tok *oauth2.Token) (string, error) {
  	info, err := googleoauth.GetTokenInfo(ctx, googleoauth.TokenInfoParams{
  		AccessToken: tok.AccessToken,
  	})
  	if err != nil {
  		return "", err
  	}
  	if info.Email == "" {
  		return NoEmail, nil
  	}
  	return info.Email, nil
  }
docs: // grabEmail fetches an email associated with the given token.
  //
  // May return (NoEmail, nil) if the token can't be resolved into an email.