[GO] Authentication process with gRPC and Firebase Authentication

Introduction

I will show you how to process authentication on Go server using gRPC and Firebase Authentication. I will write about the authorization process in another article.

Firebase Authentication You can add the SDK from the following command.

go get firebase.google.com/go

Refer to the following for initializing the Firebase Admin SDK for Go. Add the Firebase Admin SDK to your server (https://firebase.google.com/docs/admin/setup?hl=ja#initialize_the_sdk)

In the past, it seems that initialization using ```option.WithCredentialsFile ()` `` was common, but it seems that initialization using the GOOGLE_APPLICATION_CREDENTIALS environment variable is strongly recommended.

firebase.go

package middleware

import (
	"context"
	firebase "firebase.google.com/go"
	"firebase.google.com/go/auth"
)

type Firebase struct {
	Auth *auth.Client
}

func NewFirebase() (inst *Firebase, err error) {
	inst = new(Firebase)
	// GOOGLE_APPLICATION_Implicitly read the credential file specified by CREDENTIALS
	app, err := firebase.NewApp(context.Background(), nil)
	if err != nil {
		return
	}
	authInst, err := app.Auth(context.Background())
	if err != nil {
		return
	}

	inst.Auth = authInst
	return
}

Authentication process

This is the definition of a receiver that has an authentication method to use as an argument in grpc_auth.UnaryServerInterceptor, which will be explained later. Have the Firebase in the field.

package middleware

import (
	"context"
	grpc_auth "github.com/grpc-ecosystem/go-grpc-middleware/auth"
)

type Authentication struct {
	firebase Firebase
}

func NewAuthentication(firebase Firebase) *Authentication {
	authInst := new(Authentication)
	authInst.firebase = firebase
	return authInst
}

func (au *Authentication) Authenticate(ctx context.Context) (newCtx context.Context, err error) {

	idToken, err := grpc_auth.AuthFromMD(ctx, "bearer")

	//JWT verification
	token, err := au.firebase.Auth.VerifyIDToken(context.Background(), idToken)
	if err != nil {
		return
	}
	//Return JWT information in the key token in the context of the argument
	newCtx = context.WithValue(ctx, "token", token.Claims)
	return
}

By the way, this article was easy to understand, so I will share it as a reference. If you read the explanation about Interceptor, you can understand the contents of the subsequent processing smoothly. Try to authenticate / authorize with gRPC-Go Middleware (Inerceptor)

The middleware used for authentication uses grpc_auth as defined in Go gRPC Middleware.

main.go

package main

import (
	grpc_middleware "github.com/grpc-ecosystem/go-grpc-middleware"
	grpc_auth "github.com/grpc-ecosystem/go-grpc-middleware/auth"
	"google.golang.org/grpc"
	"google.golang.org/grpc/reflection"
	"log"
	pb "my-project/grpc"
	"my-project/middleware"
	"net"
)

func main() {

	listenPort, err := net.Listen("tcp", ":800")
	if err != nil {
		log.Fatalln(err)
	}

	//Create a Firebase instance
	firebase, err := NewFirebase()
	if err != nil {
		log.Fatalln(err)
	}
	//Create an Authentication instance
	auth = *NewAuthentication(*firebase)

	//Add authentication settings to server
	server := grpc.NewServer(
		grpc_middleware.WithUnaryServerChain(
			grpc_auth.UnaryServerInterceptor(auth),
		),
		//Required when using Streaming
		grpc_middleware.WithStreamServerChain(
			grpc_auth.StreamServerInterceptor(auth),
		))

	pb.MyProjectServer(server, &handler)

	reflection.Register(server)

	if err := server.Serve(listenPort); err != nil {
		log.Fatalf("failed to serve: %v", err)
	}
}

Summary

It was a simple way to authenticate with a Go server using gRPC and Firebase Authentication. Authorization can be implemented in Interceptor in a similar way, so I'll draw it in another article.