JSON Web Token Authentication with C++

This guide provides steps to implement JSON Web Token (JWT) authentication in C++ for user authentication, including how to create and verify tokens using popular C++ libraries.

In this article, we will learn how to implement JSON Web Token (JWT) authentication in C++ to secure APIs. JWT allows encoding authentication information into a token, enabling secure and verifiable user identification in applications.

C++ Code

#include <iostream>
#include <jwt-cpp/jwt.h>  // Requires jwt-cpp library

int main() {
    // Create a JSON Web Token (JWT)
    auto token = jwt::create()
                    .set_issuer("auth0")
                    .set_type("JWT")
                    .set_payload_claim("user", jwt::claim(std::string("John Doe")))
                    .set_expires_at(std::chrono::system_clock::now() + std::chrono::seconds{3600})
                    .sign(jwt::algorithm::hs256{"secret_key"});

    std::cout << "Generated JWT: " << token << std::endl;

    // Verify the JWT
    auto decoded = jwt::decode(token);
    auto verifier = jwt::verify()
                        .allow_algorithm(jwt::algorithm::hs256{"secret_key"})
                        .with_issuer("auth0");

    try {
        verifier.verify(decoded);  // Verify token
        std::cout << "Token is valid!" << std::endl;
    } catch (const std::exception& e) {
        std::cerr << "Invalid token: " << e.what() << std::endl;
    }

    return 0;
}

Detailed explanation:

1. #include <jwt-cpp/jwt.h>: Includes the jwt-cpp library to work with JWTs.
2. jwt::create(): Starts creating a new JWT token.
3. set_issuer("auth0"): Sets the token issuer.
4. set_payload_claim("user", ...): Sets the user information to be encoded in the token.
5. set_expires_at(...): Sets the token expiration time.
6. sign(jwt::algorithm::hs256{"secret_key"}): Signs the token with HMAC-SHA256 using a secret key.
7. jwt::decode(token): Decodes the token to verify.
8. jwt::verify().allow_algorithm(...): Verifies the token with the algorithm and secret key.
9. verifier.verify(decoded): Performs the verification of the decoded token.

System requirements:

• C++ version: C++11 or later.
• jwt-cpp library: Install using a package manager or manually from GitHub.
• A C++ compiler supporting C++11 or later.

How to install the library:

• To install the jwt-cpp library, you can clone it from GitHub: https://github.com/Thalhammer/jwt-cpp.
• Add the library path to your CMakeLists.txt if using CMake:

target_link_libraries(your_project jwt-cpp)

Tips:

• JWTs should be handled carefully; avoid exposing the secret key (secret_key).
• Always use HTTPS when transmitting tokens to prevent leakage of sensitive information.

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