SocialPub/PrivaPub.Tests/Federation/HttpSignaturesTests.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;

using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Signing;

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

namespace PrivaPub.Tests.Federation
{
	public class HttpSignaturesTests
	{
		const string Host = "privapub.test";
		const string KeyId = "https://mastodon.example/users/alice#main-key";
		static readonly DateTimeOffset Now = new(2026, 10, 1, 12, 0, 0, TimeSpan.Zero);
		static readonly byte[] Body = Encoding.UTF8.GetBytes("""{"type":"Follow","actor":"https://mastodon.example/users/alice"}""");

		readonly RSA _key = RSA.Create(2048);

		string PublicKey => _key.ExportSubjectPublicKeyInfoPem();

		DefaultHttpContext MastodonRequest(string signedTarget = "/peasants/bob/mouth", DateTimeOffset? signedAt = default,
			string headers = "(request-target) host date digest content-type", byte[] signedBody = default, string extra = "")
		{
			var date = (signedAt ?? Now).ToString("r", CultureInfo.InvariantCulture);
			var digest = HttpSignatures.Digest(signedBody ?? Body);
			var values = new Dictionary<string, string>
			{
				["(request-target)"] = $"post {signedTarget}",
				["host"] = Host,
				["date"] = date,
				["digest"] = digest,
				["content-type"] = "application/activity+json"
			};
			var signingString = string.Join("\n", headers.Split(' ').Select(h => $"{h}: {values[h]}"));
			var signature = Convert.ToBase64String(_key.SignData(Encoding.UTF8.GetBytes(signingString), HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1));

			var context = new DefaultHttpContext();
			context.Request.Method = "POST";
			context.Request.Host = new HostString(Host);
			context.Request.Path = "/peasants/bob/mouth";
			context.Features.Get<IHttpRequestFeature>().RawTarget = "/peasants/bob/mouth";
			context.Request.Headers["Date"] = date;
			context.Request.Headers["Digest"] = digest;
			context.Request.Headers["Content-Type"] = "application/activity+json";
			context.Request.Headers["Signature"] = $"keyId=\"{KeyId}\",algorithm=\"rsa-sha256\",headers=\"{headers}\",signature=\"{signature}\"{extra}";
			return context;
		}

		string Check(HttpContext context, byte[] body = default)
		{
			var parameters = HttpSignatures.Parse(context.Request.Headers["Signature"].ToString());
			var problem = HttpSignatures.CheckRequest(context.Request, parameters, body ?? Body, Now);
			if (problem != default)
				return problem;
			return HttpSignatures.Verify(PublicKey, HttpSignatures.SigningString(context.Request, parameters), parameters.Signature)
				? default
				: "does not verify";
		}

		[Fact]
		public void Accepts_a_mastodon_style_delivery() =>
			Assert.Null(Check(MastodonRequest()));

		[Fact]
		public void Refuses_a_tampered_body() =>
			Assert.Equal("the digest does not match the body", Check(MastodonRequest(), Encoding.UTF8.GetBytes("""{"type":"Delete"}""")));

		[Fact]
		public void Refuses_a_signature_for_another_inbox() =>
			Assert.Equal("does not verify", Check(MastodonRequest(signedTarget: "/peasants/carol/mouth")));

		[Fact]
		public void Refuses_a_signature_older_than_an_hour() =>
			Assert.Equal("the Date header is outside the allowed window", Check(MastodonRequest(signedAt: Now.AddMinutes(-61))));

		[Fact]
		public void Accepts_a_clock_slightly_ahead() =>
			Assert.Null(Check(MastodonRequest(signedAt: Now.AddMinutes(10))));

		[Fact]
		public void Refuses_a_clock_far_ahead() =>
			Assert.Equal("the Date header is outside the allowed window", Check(MastodonRequest(signedAt: Now.AddMinutes(20))));

		[Fact]
		public void Refuses_a_signature_without_the_request_target() =>
			Assert.Equal("(request-target) is not signed", Check(MastodonRequest(headers: "host date digest")));

		[Fact]
		public void Refuses_a_signature_without_the_host() =>
			Assert.Equal("host is not signed", Check(MastodonRequest(headers: "(request-target) date digest")));

		[Fact]
		public void Refuses_a_body_whose_digest_is_not_signed() =>
			Assert.Equal("the digest is not signed", Check(MastodonRequest(headers: "(request-target) host date")));

		[Fact]
		public void Refuses_an_expired_signature() =>
			Assert.Equal("the signature has expired",
				Check(MastodonRequest(extra: $",expires=\"{Now.AddMinutes(-20).ToUnixTimeSeconds()}\"")));

		[Fact]
		public void Signs_with_the_raw_request_target()
		{
			var context = MastodonRequest(signedTarget: "/peasants/b%6Fb/mouth");
			context.Features.Get<IHttpRequestFeature>().RawTarget = "/peasants/b%6Fb/mouth";

			Assert.Null(Check(context));
		}

		[Fact]
		public void Verifies_its_own_outbound_signature()
		{
			var (privateKey, publicKey) = Keys.NewKeyPair();
			var signer = new LocalActor { UserName = "bob", BaseAddress = "https://privapub.test", PrivateKeyPem = privateKey };
			using var outbound = new HttpRequestMessage(HttpMethod.Post, "https://mastodon.example/users/alice/inbox");
			HttpSignatures.Sign(outbound, signer, Body);

			var context = new DefaultHttpContext();
			context.Request.Method = "POST";
			context.Request.Host = new HostString("mastodon.example");
			context.Request.Path = "/users/alice/inbox";
			context.Features.Get<IHttpRequestFeature>().RawTarget = "/users/alice/inbox";
			foreach (var header in outbound.Headers)
				context.Request.Headers[header.Key] = string.Join(", ", header.Value);
			var parameters = HttpSignatures.Parse(context.Request.Headers["Signature"].ToString());

			Assert.Equal("https://privapub.test/peasants/bob#main-key", parameters.KeyId);
			Assert.Null(HttpSignatures.CheckRequest(context.Request, parameters, Body));
			Assert.True(HttpSignatures.Verify(publicKey, HttpSignatures.SigningString(context.Request, parameters), parameters.Signature));
		}
	}
}