func FromFile(path string, opts ...Option) (*GServiceAccount, error) {
	buf, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, err
	}

	return FromJSON(buf, opts...)
}
func FromFile(path string, opts ...Option) (*GServiceAccount, error) {
	buf, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, err
	}

	return FromJSON(buf, opts...)
}
// FromFile loads Google service account credentials from a reader.