SocialPub/PrivaPub.Tests/Http/MessageSignatureTests.cs

using MongoDB.Entities;

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

using PrivaPub.Federation.Signing;
using PrivaPub.Models.Post;
using PrivaPub.Tests.Support;
using PrivaPub.Tests.Support.Host;

using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Nodes;

namespace PrivaPub.Tests.Http
{
	// RFC 9421 message signatures, as WordPress's ActivityPub plugin, Ghost and Fedify send them first: a delivery so signed
	// is taken in one request, and refused when its body or its target is not what was signed
	[Trait("Category", "Integration")]
	public sealed class MessageSignatureTests : IAsyncLifetime
	{
		PrivaPubHost _host;
		Peer _peer;

		static CancellationToken Token => TestContext.Current.CancellationToken;

		public async ValueTask InitializeAsync()
		{
			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
			_host = await PrivaPubHost.Shared();
			_peer = await Peer.Start();
		}

		public async ValueTask DisposeAsync()
		{
			if (_peer != default)
				await _peer.DisposeAsync();
		}

		[Fact]
		public async Task A_delivery_signed_as_rfc9421_is_taken_and_one_whose_body_or_target_differs_is_refused()
		{
			var alice = await _host.Mastodon("alice");
			var bob = new RemoteActor(_peer, "bob");
			var create = bob.Create("<p>signed the new way</p>", new[] { alice.Uri });
			var noteId = create["object"]!["id"]!.GetValue<string>();
			using var client = _host.Client();

			var tampered = bob.MessageSignedPost(alice.Mouth, create);
			tampered.Content = new ByteArrayContent(Encoding.UTF8.GetBytes(create.ToJsonString().Replace("new way", "other way")));
			tampered.Content.Headers.TryAddWithoutValidation("Content-Type", "application/activity+json");
			tampered.Content.Headers.TryAddWithoutValidation("Content-Digest", bob.MessageSignedPost(alice.Mouth, create).Content!.Headers.GetValues("Content-Digest").First());
			Assert.Equal(HttpStatusCode.Unauthorized, (await client.SendAsync(tampered, Token)).StatusCode);
			var elsewhere = bob.MessageSignedPost(alice.Mouth, create, signedFor: "/human-centipede");
			Assert.Equal(HttpStatusCode.Unauthorized, (await client.SendAsync(elsewhere, Token)).StatusCode);

			Assert.Equal(HttpStatusCode.Accepted, (await client.SendAsync(bob.MessageSignedPost(alice.Mouth, create), Token)).StatusCode);
			Assert.Equal(1, await _host.RunInbox(Id(create), Token));
			Assert.Contains("signed the new way", (await DB.Default.Find<Post>().Match(p => p.ObjectURI == noteId).ExecuteSingleAsync(Token)).ContentHtml);
		}

		static string Id(JsonObject activity) => activity["id"]!.GetValue<string>();

		// a signed fetch (a GET, no body) verifies the same way, and so does RSA-PSS with SHA-512
		[Fact]
		public void A_signed_fetch_and_an_rsa_pss_signature_verify()
		{
			using var key = RSA.Create(2048);
			var message = new HttpRequestMessage(HttpMethod.Get, "https://privapub.test/peasants/alice/scribbles/1");
			MessageSignatures.Sign(message, "https://peer.example/users/bob#main-key", key.ExportPkcs8PrivateKeyPem(), body: null);
			var request = Request(message);
			var signature = RequestSignature.Of(request);
			Assert.Equal("rfc9421:rsa-v1_5-sha256", signature.Scheme);
			Assert.Null(signature.Problem(request, body: null));
			Assert.True(signature.VerifiedBy(key.ExportSubjectPublicKeyInfoPem(), signature.Signed(request, "https://privapub.test")));
			Assert.False(signature.VerifiedBy(key.ExportSubjectPublicKeyInfoPem(), signature.Signed(request, "https://elsewhere.example")));

			var created = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
			var parameters = $"(\"@method\" \"@target-uri\");created={created};keyid=\"bob\";alg=\"rsa-pss-sha512\"";
			var signatureBase = $"\"@method\": GET\n\"@target-uri\": https://privapub.test/peasants/alice/scribbles/1\n\"@signature-params\": {parameters}";
			var signed = key.SignData(Encoding.UTF8.GetBytes(signatureBase), HashAlgorithmName.SHA512, RSASignaturePadding.Pss);
			var pss = new HttpRequestMessage(HttpMethod.Get, "https://privapub.test/peasants/alice/scribbles/1");
			pss.Headers.TryAddWithoutValidation("Signature-Input", $"pss={parameters}");
			pss.Headers.TryAddWithoutValidation("Signature", $"pss=:{Convert.ToBase64String(signed)}:");
			var pssRequest = Request(pss);
			var pssSignature = RequestSignature.Of(pssRequest);
			Assert.True(pssSignature.VerifiedBy(key.ExportSubjectPublicKeyInfoPem(), pssSignature.Signed(pssRequest, "https://privapub.test")));
		}

		static HttpRequest Request(HttpRequestMessage message)
		{
			var context = new DefaultHttpContext();
			context.Request.Method = message.Method.Method;
			context.Request.Host = new HostString(message.RequestUri!.Host);
			context.Request.Path = message.RequestUri.AbsolutePath;
			context.Features.Get<IHttpRequestFeature>()!.RawTarget = message.RequestUri.PathAndQuery;
			foreach (var (name, values) in message.Headers)
				context.Request.Headers[name] = values.ToArray();
			return context.Request;
		}
	}
}