auth/jwt.go
func Expiration(e time.Duration) TokenOpt {
	return TokenOpt{func(o *options) {
		o.expiration = e
	}}
}
func Expiration(e time.Duration) TokenOpt {
	return TokenOpt{func(o *options) {
		o.expiration = e
	}}
}
// Expiration sets the expiration time of the auth token