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Implementing JWT (JSON Web Token) Authentication in Go

JSON Web Tokens (JWT) are a popular method for representing claims securely between two parties. In the realm of web applications, they often serve as a way to transmit identity information (as claims) from a client to a server. In this tutorial, we’ll walk through the process of implementing JWT authentication in a Go application.

1. What is JWT?

A JSON Web Token (JWT) is a compact URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is digitally signed using JSON Web Signature (JWS).

A JWT typically looks like: xxxxx.yyyyy.zzzzz

  • Header: The header (xxxxx) typically consists of two parts: the type of the token, which is JWT, and the signing algorithm.
  • Payload: The payload (yyyyy) contains the claims. Claims are statements about the subject (user).
  • Signature: To create the signature (zzzzz) part, you have to take the encoded header, the encoded payload, a secret, the algorithm specified in the header, and sign that.

2. Setting Up the Go Environment

First, you’ll need a package to work with JWTs in Go. We’ll use the package:

3. Creating JWTs in Go

Let’s create a function to generate a JWT:

package main

import (
var mySigningKey = []byte("secretpassword")
func GenerateJWT() (string, error) {
 token := jwt.New(jwt.SigningMethodHS256)
 claims := token.Claims.(jwt.MapClaims)
 claims["authorized"] = true
 claims["user"] = "John Doe"
 claims["exp"] = time.Now().Add(time.Minute * 30).Unix()
 tokenString, err := token.SignedString(mySigningKey)
 if err != nil {
  fmt.Errorf("Something went wrong: %s", err.Error())
  return "", err
 return tokenString, nil

4. Validating JWTs in Go

Now, let’s validate the JWT:

func ValidateToken(tokenString string) (*jwt.Token, error) {
	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("There was an error")
		return mySigningKey, nil

if err != nil {
  return nil, err
 return token, nil

5. Using JWTs for Authentication in a Go Web Application

Here’s a simple example integrating JWT generation and validation in a Go HTTP server:

package main

import (

func HomePage(w http.ResponseWriter, r *http.Request) {
 validToken, err := GenerateJWT()
 if err != nil {
  fmt.Fprintf(w, err.Error())
 clientToken := r.Header.Get("Token")
 if clientToken != validToken {
  fmt.Fprintf(w, "Token is not valid")
 fmt.Fprintf(w, "Hello, World!")
func handleRequests() {
 http.HandleFunc("/", HomePage)
 log.Fatal(http.ListenAndServe(":9000", nil))
func main() {

With this setup:

  • The server creates a JWT when the homepage is accessed.
  • To validate, the client needs to send the same JWT back in the header “Token”.
  • This is a basic example. In real scenarios, you’d issue a token after login and check it on each request requiring authentication.

JWTs provide a powerful and flexible method for handling authentication and authorization in web applications. In Go, thanks to packages like, implementing JWT-based authentication is straightforward. However, always remember to keep your signing key secret and use a secure method, preferably RSA, for added security in production applications.

CGO: Embedding and C Interoperability

The Go programming language, commonly known as Golang, is designed to be simple and efficient. However, there are times when you might need to leverage existing C libraries or embed Go into other languages. This tutorial dives deep into the world of CGO — Go’s gateway to the world of C and vice versa.

1. What is CGO?

CGO enables the creation of Go packages that call C code. By using CGO with Go, you get the power to use existing C libraries and also potentially optimize performance-critical portions of your application.

To use CGO, you need to have C development tools installed on your machine. This typically includes a C compiler like gcc.

2. Calling C Code from Go

2.1 Basic Interoperability

Here’s a simple example of how to call C code from Go:

#include <stdio.h>
import "C"

func main() {
    C.puts(C.CString("Hello from C!"))

In the code above:

  • The import "C" is a special import that represents the C space.
  • The C code is wrapped in a Go multi-line string comment.
  • C.puts calls the C function puts.

2.2 Using C Structs and Functions

Suppose you have the following C code:

// mathfuncs.c

#include "mathfuncs.h"
int add(int a, int b) {
    return a + b;
// mathfuncs.h
int add(int a, int b);

You can call the add function from Go like this:

#cgo CFLAGS: -I .
#cgo LDFLAGS: -L . -lmathfuncs
#include "mathfuncs.h"
import "C"
import "fmt"

func main() {
    a, b := 3, 4
    result := C.add(,
    fmt.Printf("%d + %d = %d\n", a, b, int(result))

3. Embedding Go into Other Languages

3.1 Exporting Go Functions for C

To make Go functions accessible from C (and by extension, other languages), you can use the //export directive.

// export.go

package main
import "C"
import "fmt"
//export SayHello
func SayHello(name *C.char) {
    fmt.Printf("Hello, %s!\n", C.GoString(name))
func main() {}

After compiling this Go code into a shared library, the exported SayHello function can be called from C.

3.2 Calling Go from C

After creating a shared library using go build -o -buildmode=c-shared export.go, you can use it in C:

// main.c
#include "export.h"
int main() {
    return 0;

Compile with gcc main.c -L . -lmylib -o output.

4. Best Practices

  • Safety First: Remember that CGO can bypass Go’s memory safety. Always ensure your C code is safe and doesn’t have leaks or buffer overflows.
  • Performance: Crossing the Go-C boundary can be expensive in terms of performance. Avoid frequent transitions if possible.
  • Error Handling: Ensure you handle errors gracefully, especially when transitioning between languages.

CGO offers a powerful way to bridge Go with C, allowing you to leverage existing libraries and functionalities. With careful planning and understanding of both Go and C ecosystems, you can use CGO effectively and safely.