package main

import (
  "fmt"
  "encoding/json"
)

func main() {
  strJson := `{"key1": "value1", "key2": {"key2.1": "value2.1"}}`

  var jsonified map[string]interface{}

  json.Unmarshal([]byte(strJson), &jsonified)
  fmt.Println("%v", jsonified) // "map[key2:map[key2.1:value2.1] key1:value1]"

  fmt.Println("%v", jsonified["key2"].(map[string]interface{})["key2.1"]) // "value2.1"
}