OAuth 2.0 and JWT Authorization in C++: Complete Guide with Code

OAuth 2.0 and JWT Authorization in C++: In Practice

Modern web applications and microservices rarely do without authorization systems. The two most popular standards — OAuth 2.0 for delegating access and JWT (JSON Web Token) for compact data transfer — have become the de facto industry standard. In this article, we will break down how to implement an OAuth 2.0 client and work with JWT in C++. You will get ready-made code examples and understand how to integrate these mechanisms into your project.

What are OAuth 2.0 and JWT: A Brief Overview

OAuth 2.0 is an authorization protocol that allows applications to obtain limited access to user resources without transmitting their login and password. The main participants are: Resource Owner (user), Client (our application), Authorization Server (the server issuing tokens), and Resource Server (the server providing data).

JWT is a token format consisting of three parts: Header (signature algorithm), Payload (data, e.g., user ID or role), and Signature (signature protecting against forgery). JWT is often used as a Bearer token in OAuth 2.0.

In C++, we will use the cpprestsdk library (for HTTP requests) and jwt-cpp (for working with JWT). Install them via vcpkg:

vcpkg install cpprestsdk\nvcpkg install jwt-cpp

Implementing an OAuth 2.0 Client in C++

Let's consider a typical scenario: our C++ application needs to authenticate via Google OAuth 2.0. To do this, we need to: register the application in the Google Cloud Console, obtain a Client ID and Client Secret, and then execute the Authorization Code Flow.

Step 1: Building the Authorization URL

The first step is to redirect the user to the Google authorization page. Let's build the URL with the necessary parameters:

#include <string>\n#include <cpprest/http_client.h>\n#include <cpprest/uri_builder.h>\n\nusing namespace web;\nusing namespace web::http;\nusing namespace web::http::client;\n\nstd::string BuildAuthorizationUrl(const std::string& client_id,\n                                  const std::string& redirect_uri,\n                                  const std::string& state) {\n    uri_builder builder(U("https://accounts.google.com/o/oauth2/v2/auth"));\n    builder.append_query(U("client_id"), utility::conversions::to_string_t(client_id));\n    builder.append_query(U("redirect_uri"), utility::conversions::to_string_t(redirect_uri));\n    builder.append_query(U("response_type"), U("code"));\n    builder.append_query(U("scope"), U("openid%20email%20profile"));\n    builder.append_query(U("state"), utility::conversions::to_string_t(state));\n    builder.append_query(U("access_type"), U("offline"));\n    builder.append_query(U("prompt"), U("consent"));\n    return utility::conversions::to_utf8string(builder.to_uri().to_string());\n}

Step 2: Exchanging the Code for a Token

After the user confirms access, Google will redirect them to our redirect_uri with the code parameter. This code needs to be exchanged for an access_token and refresh_token:

pplx::task<web::json::value> ExchangeCodeForToken(\n    const std::string& client_id,\n    const std::string& client_secret,\n    const std::string& redirect_uri,\n    const std::string& code) {\n    \n    http_client client(U("https://oauth2.googleapis.com/token"));\n    \n    web::json::value body;\n    body[U("code")] = web::json::value::string(utility::conversions::to_string_t(code));\n    body[U("client_id")] = web::json::value::string(utility::conversions::to_string_t(client_id));\n    body[U("client_secret")] = web::json::value::string(utility::conversions::to_string_t(client_secret));\n    body[U("redirect_uri")] = web::json::va