Implementing OAuth 2.0 and JWT Authorization in C++ for Beginners

Introduction to OAuth 2.0 and JWT in C++

In modern web development, security and access control are critically important aspects. OAuth 2.0 and JWT (JSON Web Tokens) have become the de facto standard for implementing authorization in APIs and web applications. Despite the fact that these technologies are more often associated with JavaScript, Python, or Java, C++ also provides powerful tools for their implementation.

In this article, we will break down how OAuth 2.0 and JWT work and show practical examples of their implementation in C++. The material is aimed at beginner developers familiar with the basics of C++ and network programming.

What is OAuth 2.0?

OAuth 2.0 is an authorization protocol that allows applications to obtain limited access to user resources without transmitting their credentials (login and password). Instead, access tokens are used. The main roles in OAuth 2.0 are:

• Resource Owner — the user who owns the data.
• Client — the application requesting access.
• Authorization Server — issues tokens after successful authentication.
• Resource Server — the API protected by tokens.

What is JWT?

JWT (JSON Web Token) is a compact token format that contains a JSON object with data (claims) and is signed to verify integrity. The JWT structure consists of three parts separated by dots:

• Header — contains the token type and signing algorithm (e.g., HS256 or RS256).
• Payload — contains data (e.g., user ID, expiration time).
• Signature — created by hashing the header + payload using a secret key.

The advantage of JWT is that it is self-contained: the resource server can verify the token without contacting the authorization server, which speeds up operation.

Main Part: Implementation in C++

1. Libraries and Environment Setup

To work with OAuth 2.0 and JWT in C++, we will need the following libraries:

• cURL (libcurl) — for HTTP requests to the authorization server.
• nlohmann/json — for working with JSON.
• jwt-cpp — for creating and verifying JWT tokens.
• OpenSSL — for cryptographic operations (signing and hashing).

Installation via vcpkg (recommended):

vcpkg install curl jsoncpp jwt-cpp openssl

Example CMakeLists.txt:

cmake_minimum_required(VERSION 3.15)project(OAuthJWTExample)

find_package(CURL REQUIRED)find_package(nlohmann_json REQUIRED)find_package(jwt-cpp REQUIRED)find_package(OpenSSL REQUIRED)

add_executable(main main.cpp)target_link_libraries(main    CURL::libcurl    nlohmann_json::nlohmann_json    jwt-cpp::jwt-cpp    OpenSSL::SSL    OpenSSL::Crypto)

2. Implementing OAuth 2.0 Authorization Code Flow

Let's consider the most common flow — the Authorization Code Flow. The client receives an authorization code from the user and then exchanges it for an access token.

Step 1: Redirecting the user to the authorization server (simplified example):

#include <iostream>#include <string>

std::string buildAuthUrl(const std::string& clientId,                          const std::string& redirectUri) {    return "https://auth.example.com/authorize?"           "response_type=code&"           "client_id=" + clientId + "&"           "redirect_uri=" + redirectUri + "&"           "scope=openid+profile";}

int main() {    std::string clientId = "your_client_id";    std::string redirectUri = "http://lo