auth/jwt.go
func Claimer(c func(claims *jwt.StandardClaims) jwt.Claims) TokenOpt {
	return TokenOpt{func(o *options) {
		o.claimer = c
	}}
}
func Claimer(c func(claims *jwt.StandardClaims) jwt.Claims) TokenOpt {
	return TokenOpt{func(o *options) {
		o.claimer = c
	}}
}
// Claimer is responsible for transforming a standard claims object into a
// custom one.