OAuth 2.0 and JWT Authorization in C++: A Complete Guide

Introduction to OAuth 2.0 and JWT Authorization in C++

In the modern world of web development, security and authentication convenience play a key role. OAuth 2.0 and JWT (JSON Web Tokens) have become de facto standards for implementing authorization in distributed systems. In this article, we will look at how to implement OAuth 2.0 and JWT authorization in C++ — a powerful and high-performance language often used for building high-load server applications.

Despite the fact that C++ is not a typical choice for web development, its performance and memory control make it ideal for creating API gateways, microservices, and real-time systems. We will show how to use modern C++ libraries for working with HTTP, JSON, and cryptography to build a reliable authorization system.

Basics of OAuth 2.0

OAuth 2.0 is an authorization protocol that allows applications to obtain limited access to user resources without transferring their credentials. The main roles in OAuth 2.0 are:

• Resource Owner — the user who owns the resources
• Client — the application requesting access
• Authorization Server — the server issuing tokens
• Resource Server — the server providing protected resources

The main grant types of OAuth 2.0 are:

• Authorization Code — for server-side applications
• Client Credentials — for service-to-service authentication
• Implicit — deprecated, for SPAs
• Resource Owner Password Credentials — for trusted clients

Implementing an OAuth 2.0 Client in C++

For working with HTTP in C++, we will use the cpp-httplib library. Consider an example of obtaining an access token via the Client Credentials grant type:

#include <httplib.h>#include <nlohmann/json.hpp>#include <iostream>

using json = nlohmann::json;

std::string get_access_token(const std::string& client_id,                             const std::string& client_secret,                             const std::string& token_url) {    httplib::Client cli(token_url);        // Form the request body    std::string body = "grant_type=client_credentials&"                       "client_id=" + client_id + "&"                       "client_secret=" + client_secret;        auto res = cli.Post("/token", body, "application/x-www-form-urlencoded");        if (res && res->status == 200) {        json response = json::parse(res->body);        return response["access_token"];    }        throw std::runtime_error("Failed to get access token");}

JWT (JSON Web Tokens)

JWT is a compact and self-contained way to transmit information between parties as a JSON object. The token consists of three parts:

• Header — contains the token type and signing algorithm
• Payload — contains claims about the user
• Signature — signature for verification

Generating JWT in C++

For working with JWT and cryptography in C++, we use the jwt-cpp and OpenSSL libraries. Example of generating a JWT with the HS256 algorithm:

#include <jwt-cpp/jwt.h>#include <chrono>

std::string create_jwt(const std::string& user_id,                       const std::string& secret_key) {    auto now = std::chrono::system_clock::now();    auto exp = now + std::chrono::hours(1);        auto token = jwt::create()        .set_type("JWT")        .set_issuer("auth.example.com")        .set_subject(user_id)        .set_issued_at(now)        .set_expires_at(exp)        .set_payload_c