Unmarshal JSON object into slice of structs with key and value

I am still learning GO and I am stumped by the following problem:
I receive a JSON string that I want to unmarshal in GO.
The JSON looks like this

{
  "MAINKEY": {
    "key1": 1,
    "key2": [1, 2]
  }
}

I am only interested in the contents of the MAINKEY, but similar to this question, I do not know the names of the keys, which should reflect the names of the map.

In the end, I want to have the following object:

type Result struct {
	Key   string
	Value []int
}

expectedResult := []Result{
	{"key1", []int{1}},
	{"key2", []int{1, 2}},
}
fmt.Printf("WANT: %+v\n", expectedResult)
//> WANT: [{Key:key1 Value:[1]} {Key:key2 Value:[1 2]}]

If possible, I don't want to unmarshal into a map[string]interface{} first (but if there is no other way, that would be ok too).

Full code so far is:

package main

import (
	"encoding/json"
	"fmt"
)

// does produce expected result at the moment...
type Result struct {
	Key   string
	Value []int
}

type Outer struct {
	Key Result `json:"MAINKEY"`
}

func main() {

	input := `{"MAINKEY": {"key1": 1, "key2": [1, 2]}}`

	var cont Outer
	json.Unmarshal([]byte(input), &cont)
	fmt.Printf("GOT: %+v\n", cont)

	expectedResult := []Result{
		{"key1", []int{1}},
		{"key2", []int{1, 2}},
	}
	fmt.Printf("WANT: %+v\n", expectedResult)
}

You can use a custom unmarshaler with a map:

type ResultList []Result

func (ls *ResultList) UnmarshalJSON(data []byte) error {
	var obj map[string]json.RawMessage
	if err := json.Unmarshal(data, &obj); err != nil {
		return err
	}

	for key, raw := range obj {
		r := Result{Key: key}
		if raw[0] == '[' { // assume array of ints
			if err := json.Unmarshal(raw, &r.Value); err != nil {
				return err
			}
		} else { // assume single int
			var i int
			if err := json.Unmarshal(raw, &i); err != nil {
				return err
			}
			r.Value = append(r.Value, i)
		}
		*ls = append(*ls, r)
	}
	return nil
}

https://go.dev/play/p/Epd6cLwyWUm

Or, if you need to retain the order, you can tokenize the input:

type ResultList []Result

func (ls *ResultList) UnmarshalJSON(data []byte) error {
	d := json.NewDecoder(bytes.NewReader(data))
	i := -1
	for {
		t, err := d.Token()
		if err == io.EOF {
			break
		}
		if err != nil {
			return err
		}

		switch v := t.(type) {
		case string:
			*ls = append(*ls, Result{Key: v})
			i += 1
		case float64:
			(*ls)[i].Value = append((*ls)[i].Value, int(v))
		}
	}
	return nil
}

https://go.dev/play/p/nABjw5IHZ7R