we should add PQC tests to SslStream

[wfurt]

as the new algorithms becoming more available we should improve test coverage for SslStream

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[rzikm]

PQC are covered by tests that use CertificateAuthority.BuildPrivatePki (we have lots of them). Unless explicitly specified, the test helper picks a random key type based on the test name hash

runtime/src/libraries/Common/tests/System/Security/Cryptography/X509Certificates/CertificateAuthority.cs

Lines 826 to 852 in b352164

	if (keyFactory is null)
	{
	// This could use any of the non-cryptographic hashes, but that complicates the code sharing for this file,
	// so use IncrementalHash(SHA256) as it's inbox.
	//
	// System.HashCode isn't suitable because it's randomized, and we want the algorithm to
	// be consistent for any given test from run to run.
	using (IncrementalHash hasher = IncrementalHash.CreateHash(HashAlgorithmName.SHA256))
	{
	// The use of AsBytes means that the hash value will differ between Big and Little Endian
	// platforms, but that's OK: a failing test in a given configuration will continue to fail
	// in that configuration.
	hasher.AppendData(MemoryMarshal.AsBytes(new ReadOnlySpan<PkiOptions>(ref pkiOptions)));
	hasher.AppendData(MemoryMarshal.AsBytes(new ReadOnlySpan<int>(ref intermediateAuthorityCount)));
	hasher.AppendData(MemoryMarshal.AsBytes(testName.AsSpan()));
	hasher.AppendData(MemoryMarshal.AsBytes(subjectName.AsSpan()));
	Span<byte> hash = stackalloc byte[256 / 8];
	int written = hasher.GetCurrentHash(hash);
	Debug.Assert(written == hash.Length);
	// Using mod here will create an imbalance any time the key factories array isn't a power of 2,
	// but that's OK.
	KeyFactory[] keyFactories = forTls ? s_tlsVariantKeyFactories : s_variantKeyFactories;
	keyFactory = keyFactories[hash[0] % keyFactories.Length];
	}
	}

It has already caught some errors in the past

• OpenSSL error - unknown certificate type when using SLH-DSA-* certificates #119573
• ML-DSA certificates cannot be used with QUIC and HTTP/3 #119641

Is there something else you had in mind?