Firebase JWT authentication : Sample functions for token verification

main.go

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"strings"
	"time"

	firebase "firebase.google.com/go/v4"
	"firebase.google.com/go/v4/auth"
	"github.com/gin-contrib/cors"
	"github.com/gin-gonic/gin"
	"github.com/rahul-yr/learn-go-grapql/graph"
	"google.golang.org/api/option"
)

func authCheckerMiddleware(client *auth.Client) gin.HandlerFunc {
	return func(c *gin.Context) {
		// get token from request header
		token := c.Request.Header.Get("Authorization")
		if token == "" {
			c.AbortWithStatus(401)
			return
		}
		// split bearer token
		splitToken := strings.Split(token, "Bearer ")
		token = splitToken[1]
		// Check if user is authenticated
		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		// get user from token
		authDetails, err := client.VerifyIDToken(ctx, token)
		if err != nil {
			log.Printf("error verifying ID token: %v\n", err)
			c.AbortWithStatus(401)
			return
		}
		log.Printf("Verified ID token: %v\n", authDetails)
		c.Next()
	}
}

func setupFirebaseAdmin() (*auth.Client, error) {
	opt := option.WithCredentialsFile("C:/Users/rahul/Downloads/sa.json")
	app, err := firebase.NewApp(context.Background(), nil, opt)
	if err != nil {
		return nil, fmt.Errorf("error initializing app: %v", err)
	}
	client, err := app.Auth(context.Background())
	if err != nil {
		log.Fatalf("error getting Auth client: %v\n", err)
		return nil, err
	}
	return client, nil
}

// main is the entry point for the application.
func main() {
	app, err := setupFirebaseAdmin()
	if err != nil {
		log.Fatalf("error initializing app: %v", err)
	}
	// gin setup
	gin.SetMode(gin.ReleaseMode)
	// create gin engine
	router := gin.Default()
	// add recovery middleware
	// router.Use(gin.Recovery())
	// add custom middleware
	router.Use(authCheckerMiddleware(app))
	// enable cors
	router.Use(cors.Default())
	// create graphql endpoint
	router.POST("/todo", graph.TodoGraphRouter)
	// add webserver port
	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
	}
	// start webserver
	router.Run(":" + port)
}