[Golang] Mask struct by role using struct tag

main.go

package main

import (
	"encoding/json"
	"fmt"
	"os"
	"reflect"
	"strings"
)

type response struct {
	ID       string `json:"id"`
	Username string `json:"username"`
	Password string `json:"password,omitempty" role:"admin"`
	Info     *info  `json:"info,omitempty" role:"admin,officer"`
}

type info struct {
	FirstName string `json:"first_name,omitempty" role:"admin,officer"`
	LastName  string `json:"last_name"`
}

func makeResponse() *response {
	return &response{
		ID:       "10",
		Username: "user1",
		Password: "1234",
		Info: &info{
			FirstName: "AAA",
			LastName:  "BBB",
		},
	}
}

// $ go run main.go
// Raw struct:
// {"id":"10","username":"user1","password":"1234","info":{"first_name":"AAA","last_name":"BBB"}}
// Mask for admin:
// {"id":"10","username":"user1","password":"1234","info":{"first_name":"AAA","last_name":"BBB"}}
// Mask for marketing:
// {"id":"10","username":"user1"}
// Mask for officer:
// {"id":"10","username":"user1","info":{"first_name":"AAA","last_name":"BBB"}}
func main() {
	r := makeResponse()

	fmt.Println("Raw struct:")
	json.NewEncoder(os.Stdout).Encode(r)
	maskResponse(r, "admin")
	fmt.Println("Mask for admin:")
	json.NewEncoder(os.Stdout).Encode(r)

	r = makeResponse()
	fmt.Println("Mask for marketing:")
	maskResponse(r, "marketing")
	json.NewEncoder(os.Stdout).Encode(r)

	r = makeResponse()
	fmt.Println("Mask for officer:")
	maskResponse(r, "officer")
	json.NewEncoder(os.Stdout).Encode(r)
}

// v must be pointer of struct
func maskResponse(v interface{}, role string) {
	rv := reflect.ValueOf(v).Elem()
	rt := reflect.TypeOf(v).Elem()

	for i := 0; i < rt.NumField(); i++ {
		ft := rt.Field(i)
		r := ft.Tag.Get("role")

		// allow for all role
		if r == "" {
			// nest struct
			if ft.Type.Kind() == reflect.Struct {
				maskResponse(rv.Field(i).Addr().Interface(), role)
			}
			continue
		}

		rs := strings.Split(r, ",")
		// not allow
		if !stringsContain(rs, role) {
			rv.Field(i).Set(reflect.New(ft.Type).Elem())
			continue
		}

		// allow but might not allow inside nest struct
		if ft.Type.Kind() == reflect.Struct {
			maskResponse(rv.Field(i).Addr().Interface(), role)
		}
	}
}

func stringsContain(xs []string, x string) bool {
	for _, p := range xs {
		if p == x {
			return true
		}
	}
	return false
}