Minifycode 2023-10-13 Viewed 240 times C#

To generate a code_challenge from a code_verifier for use in an OAuth 2.0 authorization request to Auth0, you'll typically need to follow the PKCE (Proof Key for Code Exchange) protocol. This involves creating a SHA-256 hash of the code_verifier, and then encoding the hash in base64 URL-safe encoding.

Here's a C# example of how to generate a code_challenge:


using System;
using System.Security.Cryptography;
using System.Text;

class Program
    static void Main()
        // Generate a random code verifier
        string codeVerifier = GenerateCodeVerifier();

        // Generate the code challenge
        string codeChallenge = GenerateCodeChallenge(codeVerifier);

        Console.WriteLine("Code Verifier: " + codeVerifier);
        Console.WriteLine("Code Challenge: " + codeChallenge);

    static string GenerateCodeVerifier()
        // Generate a random string (typically 43-128 characters in length)
        // You can use a library to generate a random string, e.g., Guid.NewGuid().ToString("N")
        string codeVerifier = "your_random_code_verifier_here";

        return codeVerifier;

    static string GenerateCodeChallenge(string codeVerifier)
        // Create a SHA-256 hash of the code_verifier
        using (SHA256 sha256 = SHA256.Create())
            byte[] codeVerifierBytes = Encoding.ASCII.GetBytes(codeVerifier);
            byte[] codeChallengeBytes = sha256.ComputeHash(codeVerifierBytes);

            // Encode the hash in base64 URL-safe encoding
            string codeChallenge = Base64UrlEncode(codeChallengeBytes);

            return codeChallenge;

    static string Base64UrlEncode(byte[] data)
        string base64 = Convert.ToBase64String(data);
        string base64Url = base64.Replace("+", "-").Replace("/", "_").TrimEnd('=');
        return base64Url;

How to generate a code_challenge from the code_verifier in c#
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