git.stella-ops.org/tests/Provenance/StellaOps.Provenance.Attestation.Tests/SignersTests.cs

using System.Text;
using StellaOps.Provenance.Attestation;
using Xunit;

namespace StellaOps.Provenance.Attestation.Tests;

public sealed class SignersTests
{
    [Fact]
    public async Task HmacSigner_SignsAndAudits()
    {
        var key = new InMemoryKeyProvider("k1", Convert.FromHexString("0f0e0d0c0b0a09080706050403020100"));
        var audit = new InMemoryAuditSink();
        var time = new TestTimeProvider(new DateTimeOffset(2025, 11, 22, 12, 0, 0, TimeSpan.Zero));
        var signer = new HmacSigner(key, audit, time);

        var request = new SignRequest(Encoding.UTF8.GetBytes("payload"), "application/json",
            Claims: new Dictionary<string, string> { { "sub", "builder" } });

        var result = await signer.SignAsync(request);

        Assert.Equal("k1", result.KeyId);
        Assert.Equal(time.GetUtcNow(), result.SignedAt);
        Assert.Equal(
            Convert.FromHexString("b3ae92d9a593318d03d7c4b6dca9710c416f582e88cfc08196d8c2cdabb3c480"),
            result.Signature);
        Assert.Single(audit.Signed);
        Assert.Empty(audit.Missing);
    }

    [Fact]
    public async Task HmacSigner_EnforcesRequiredClaims()
    {
        var key = new InMemoryKeyProvider("k-claims", Encoding.UTF8.GetBytes("secret"));
        var audit = new InMemoryAuditSink();
        var signer = new HmacSigner(key, audit, new TestTimeProvider(DateTimeOffset.UtcNow));

        var request = new SignRequest(Encoding.UTF8.GetBytes("payload"), "text/plain",
            Claims: new Dictionary<string, string>(),
            RequiredClaims: new[] { "sub" });

        await Assert.ThrowsAsync<InvalidOperationException>(() => signer.SignAsync(request));
        Assert.Contains(audit.Missing, x => x.keyId == "k-claims" && x.claim == "sub");
    }

    [Fact]
    public async Task RotatingKeyProvider_LogsRotationWhenNewKeyBecomesActive()
    {
        var now = new DateTimeOffset(2025, 11, 22, 10, 0, 0, TimeSpan.Zero);
        var time = new TestTimeProvider(now);
        var audit = new InMemoryAuditSink();

        var expiring = new InMemoryKeyProvider("old", new byte[] { 0x01 }, now.AddMinutes(5));
        var longLived = new InMemoryKeyProvider("new", new byte[] { 0x02 }, now.AddHours(1));

        var provider = new RotatingKeyProvider(new[] { expiring, longLived }, time, audit);
        var signer = new HmacSigner(provider, audit, time);

        await signer.SignAsync(new SignRequest(new byte[] { 0xAB }, "demo"));

        Assert.Contains(audit.Rotations, r => r.previousKeyId == "old" && r.nextKeyId == "new");
        Assert.Equal("new", provider.KeyId);
    }

    [Fact]
    public async Task CosignSigner_UsesClientAndAudits()
    {
        var signatureBytes = Convert.FromBase64String(await File.ReadAllTextAsync(Path.Combine("Fixtures", "cosign.sig"))); // fixture is deterministic
        var client = new FakeCosignClient(signatureBytes);
        var audit = new InMemoryAuditSink();
        var time = new TestTimeProvider(new DateTimeOffset(2025, 11, 22, 13, 0, 0, TimeSpan.Zero));
        var signer = new CosignSigner("cosign://stella", client, audit, time);

        var request = new SignRequest(Encoding.UTF8.GetBytes("subject"), "application/vnd.stella+json",
            Claims: new Dictionary<string, string> { { "sub", "artifact" } },
            RequiredClaims: new[] { "sub" });

        var result = await signer.SignAsync(request);

        Assert.Equal(signatureBytes, result.Signature);
        Assert.Equal(time.GetUtcNow(), result.SignedAt);
        Assert.Equal("cosign://stella", result.KeyId);
        Assert.Single(audit.Signed);
        Assert.Empty(audit.Missing);

        var call = Assert.Single(client.Calls);
        Assert.Equal("cosign://stella", call.keyRef);
        Assert.Equal("application/vnd.stella+json", call.contentType);
        Assert.Equal(request.Payload, call.payload);
    }

    [Fact]
    public async Task KmsSigner_EnforcesRequiredClaims()
    {
        var signature = new byte[] { 0xCA, 0xFE, 0xBA, 0xBE };
        var client = new FakeKmsClient(signature);
        var audit = new InMemoryAuditSink();
        var key = new InMemoryKeyProvider("kms-1", new byte[] { 0x00 }, DateTimeOffset.UtcNow.AddDays(1));
        var signer = new KmsSigner(client, key, audit, new TestTimeProvider(DateTimeOffset.UtcNow));

        var request = new SignRequest(Encoding.UTF8.GetBytes("body"), "application/json",
            Claims: new Dictionary<string, string> { { "aud", "stella" } },
            RequiredClaims: new[] { "sub" });

        await Assert.ThrowsAsync<InvalidOperationException>(() => signer.SignAsync(request));
        Assert.Contains(audit.Missing, x => x.keyId == "kms-1" && x.claim == "sub");

        var validAudit = new InMemoryAuditSink();
        var validSigner = new KmsSigner(client, key, validAudit, new TestTimeProvider(DateTimeOffset.UtcNow));
        var validRequest = new SignRequest(Encoding.UTF8.GetBytes("body"), "application/json",
            Claims: new Dictionary<string, string> { { "aud", "stella" }, { "sub", "actor" } },
            RequiredClaims: new[] { "sub" });

        var result = await validSigner.SignAsync(validRequest);

        Assert.Equal(signature, result.Signature);
        Assert.Equal("kms-1", result.KeyId);
        Assert.Empty(validAudit.Missing);
    }

    private sealed class FakeCosignClient : ICosignClient
    {
        public List<(byte[] payload, string contentType, string keyRef)> Calls { get; } = new();
        private readonly byte[] _signature;

        public FakeCosignClient(byte[] signature)
        {
            _signature = signature ?? throw new ArgumentNullException(nameof(signature));
        }

        public Task<byte[]> SignAsync(byte[] payload, string contentType, string keyRef, CancellationToken cancellationToken)
        {
            Calls.Add((payload, contentType, keyRef));
            return Task.FromResult(_signature);
        }
    }

    private sealed class FakeKmsClient : IKmsClient
    {
        private readonly byte[] _signature;
        public List<(byte[] payload, string contentType, string keyId)> Calls { get; } = new();

        public FakeKmsClient(byte[] signature) => _signature = signature;

        public Task<byte[]> SignAsync(byte[] payload, string contentType, string keyId, CancellationToken cancellationToken)
        {
            Calls.Add((payload, contentType, keyId));
            return Task.FromResult(_signature);
        }
    }
}

internal sealed class TestTimeProvider : TimeProvider
{
    private DateTimeOffset _now;

    public TestTimeProvider(DateTimeOffset now) => _now = now;

    public override DateTimeOffset GetUtcNow() => _now;
    public override TimeZoneInfo LocalTimeZone => TimeZoneInfo.Utc;
    public override long GetTimestamp() => 0L;

    public void Advance(TimeSpan delta) => _now = _now.Add(delta);
}