Firebase SignInWithCustomToken

firebase_sign_in_with_custom_token.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
)

const (
	verifyCustomTokenURL = "https://www.googleapis.com/identitytoolkit/v3/relyingparty/verifyCustomToken?key=%s"
)

var (
	apiKey = os.Getenv("FIREBASE_WEB_API_KEY") // see https://console.firebase.google.comproject/<project_id>/settings/general/
)

// see https://github.com/firebase/firebase-admin-go/blob/1d2a52c3c8195451b5ad2e0a173906bd6eb9529d/integration/auth/auth_test.go#L199
func SignInWithCustomToken(token string) (string, error) {
	req, err := json.Marshal(map[string]interface{}{
		"token":             token,
		"returnSecureToken": true,
	})
	if err != nil {
		return "", err
	}

	resp, err := postRequest(fmt.Sprintf(verifyCustomTokenURL, apiKey), req)
	if err != nil {
		return "", err
	}
	var respBody struct {
		IDToken string `json:"idToken"`
	}
	if err := json.Unmarshal(resp, &respBody); err != nil {
		return "", err
	}
	return respBody.IDToken, err
}

func postRequest(url string, req []byte) ([]byte, error) {
	resp, err := http.Post(url, "application/json", bytes.NewBuffer(req))
	if err != nil {
		return nil, err
	}

	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("unexpected http status code: %d", resp.StatusCode)
	}
	return ioutil.ReadAll(resp.Body)
}

func main() {
	token, err := SignInWithCustomToken("eyJxxx")
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%s\n", token)
}