Pkce.hpp

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#pragma once
#ifndef _KURLYK_UTILS_PKCE_HPP_INCLUDED
#define _KURLYK_UTILS_PKCE_HPP_INCLUDED

 
#include "Base64Url.hpp"
#include <hmac_cpp/sha256.hpp>
#include <hmac_cpp/hmac_utils.hpp>
#include <string>
#include <vector>
#include <cstdint>
#include <algorithm>
 
namespace kurlyk {
namespace utils {

    struct PkcePair {
        std::string code_verifier;          
        std::string code_challenge;         
        std::string code_challenge_method = "S256"; 
    };

    inline std::string generate_code_verifier(std::size_t length = 64) {
        static const char allowed[] =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.~";
        if (length < 43) length = 43;
        if (length > 128) length = 128;
 
        std::vector<uint8_t> random_bytes = hmac_cpp::random_bytes(length);
        std::string verifier;
        verifier.reserve(length);
 
        const std::size_t allowed_count = sizeof(allowed) - 1; // exclude null terminator
        for (std::size_t i = 0; i < length; ++i) {
            verifier.push_back(allowed[random_bytes[i] % allowed_count]);
        }
        return verifier;
    }

    inline std::string make_s256_code_challenge(const std::string& verifier) {
        std::vector<uint8_t> digest = hmac_hash::sha256(
            reinterpret_cast<const uint8_t*>(verifier.data()),
            verifier.size());
        return base64url_encode(digest.data(), digest.size());
    }

    inline PkcePair make_pkce_pair() {
        PkcePair pair;
        pair.code_verifier = generate_code_verifier();
        pair.code_challenge = make_s256_code_challenge(pair.code_verifier);
        return pair;
    }
 
} // namespace utils
} // namespace kurlyk
 
#endif // _KURLYK_UTILS_PKCE_HPP_INCLUDED