SquareWidget.HMAC.Server.Core 1.0.0

SquareWidget.HMAC.Server.Core

Server-side HMAC authentication handler

Prerequisites

ASP.NET Core 2.1

Getting Started

Download the NuGet package in your ASP.NET Core 2.1 API. Implement a shared secret store service from abstract base class SharedSecretStoreService as in this example:

using SquareWidget.HMAC.Server.Core;
using System.Threading.Tasks;

namespace SquareWidget.ExampleApi
{
    public class MySharedSecretStoreService : SharedSecretStoreService
    {
        public override Task<string> GetSharedSecretAsync(string clientId)
        {
            // TODO: Use clientId to get the shared secret from Azure Key Vault, IdentityServer4, or a database
            return Task.Run(() => "P@ssw0rd");
        }
    }
}

Add to ConfigureServices method in Startup.cs to register the authentication handler:

services
    .AddAuthentication(HmacAuthenticationDefaults.AuthenticationScheme)
    .AddHmacAuthentication<MySharedSecretStoreService>(o => { });

Options

By default the authentication handler looks for two request headers called "Hash" and "Timestamp" but these can be overridden if the client passes in another value in the request header:

services
    .AddAuthentication(HmacAuthenticationDefaults.AuthenticationScheme)
    .AddHmacAuthentication<MySharedSecretStoreService>(o => 
    {
        o.HashHeaderName = "MyHash";
        o.TimestampHeaderName = "MyTimestamp";
    });

There is a replay attack value of 15 seconds. This can be overridden which is especially useful when stepping through code:

services
    .AddAuthentication(HmacAuthenticationDefaults.AuthenticationScheme)
    .AddHmacAuthentication<MySharedSecretStoreService>(o => 
    {
        o.ReplayAttackDelayInSeconds = 900; // 15 mins
    });

Client Side

/*
using System;
using System.Globalization;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
*/

var uri = "https://localhost:01234/api/values";
var clientId = "testClient";
var clientSecret = "P@ssw0rd";
var hashHeaderName = "Hash";
var timestampHeaderName = "Timestamp";
var timestamp = DateTime.UtcNow;
var timestampValue = timestamp.ToString("o", CultureInfo.InvariantCulture);
var ticks = timestamp.Ticks.ToString(CultureInfo.InvariantCulture);

string hashValue;
var key = Encoding.UTF8.GetBytes(clientSecret);
using (var hmac = new HMACSHA256(key))
{
    var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(ticks));
    var hashString = Convert.ToBase64String(hash);
    hashValue = string.Format("{0}:{1}", clientId, hashString);
}

var client = new HttpClient();
client.DefaultRequestHeaders.Clear();
client.DefaultRequestHeaders.Add(timestampHeaderName, timestampValue);
client.DefaultRequestHeaders.Add(hashHeaderName, hashValue);
var response = await client.GetAsync(uri);
if (response.IsSuccessStatusCode)
{
    Console.WriteLine("Received HTTP 200 from API. Writing values to console...");
    Console.WriteLine(Environment.NewLine);

    var content = await response.Content.ReadAsStringAsync();
    Console.WriteLine(content);
}
else
{
    Console.WriteLine("Response was unsuccessful with status code: " + response.StatusCode);
}

Authors

• James Still - Initial work - SquareWidget

License

This project is licensed under the MIT License and is free to use.