type ImpersonateTokenSource struct {
	// Ctx is the execution context of the impersonation process
	// used to perform http call to the URL. Required
	Ctx context.Context
	// Ts is the source credential used to generate a token on the
	// impersonated service account. Required.
	Ts oauth2.TokenSource

	// URL is the endpoint to call to generate a token
	// on behalf the service account. Required.
	URL string
	// Scopes that the impersonated credential should have. Required.
	Scopes []string
	// Delegates are the service account email addresses in a delegation chain.
	// Each service account must be granted roles/iam.serviceAccountTokenCreator
	// on the next service account in the chain. Optional.
	Delegates []string
	// TokenLifetimeSeconds is the number of seconds the impersonation token will
	// be valid for.
	TokenLifetimeSeconds int
}