Add ECDsa support in X509SecurityKey and JsonWebKeyConverter.ConvertFromX509SecurityKey

[joegoldman2]

Fixes #1943.
Fixes #2217.

[jaanclaeys]

I applaud the fix, but ...

I think we need a better solution going forward in the future. I am pretty sure we will see more algorithms in the future on certificates (Dilithium e.g.)

Problem is probably here with X509Certificate2 and the extension methods. Trying each private key method might be a bit of a performance hit.
Having an informed constructor might help here ? Or even different subclasses X509RsaSecurityKey / X509EcdsaSecurityKey, or fix this in X509Certificate2 itself ?

[joegoldman2]

I don't think that creating sub-classes is the right solution. In many cases, the algorithm of the key in the certificate is not known in advance and X509SecurityKey is helping to abstract it.
If the algorithm is known, you can simply do:

X509Certificate2 certificate = ...;
ECDsa ecdsa = certificate.GetECDsaPrivateKey();
ECDsaSecurityKey key = new ECDsaSecurityKey(ecdsa);

And no need for any new X509EcdsaSecurityKey or equivalent.

Otherwise, I agree that the current fix isn't as future-proof as we'd like, but I think it's a good first fix before perhaps a deeper refactoring.

[keegan-caruso]

Similar comment to #2379, can we add tests for this?

[joegoldman2]

Similar comment to #2379, can we add tests for this?

Can you please check the initial comment of this PR?

[keegan-caruso]

I can commit an EC cert if that is what you would like to do.

I think in-memory certs would also be fine here if we can use them. One less thing to suppress for test data.

[joegoldman2]

I generated a self-signed cert this way:

$cert = New-SelfSignedCertificate -DnsName "CN=KeyStoreTestCertificate" -KeyAlgorithm ECDSA_nistP256 -KeyExportPolicy Exportable -CertStoreLocation Cert:\CurrentUser\My
$cert | Export-PfxCertificate -FilePath "Certificate.pfx" -Password (ConvertTo-SecureString -String "abcd" -Force -AsPlainText)
$pfxBytes = [System.IO.File]::ReadAllBytes("Certificate.pfx")
$base64Cert = [System.Convert]::ToBase64String($pfxBytes)

And added a unit test.

[joegoldman2]

The unit tests are not passing yet. I'm running into a issue that I'm not sure to understand and I opened a discussion in the runtime repo: dotnet/runtime#104294.

[joegoldman2]

I updated the unit tests not to use the self-signed certificate generated by me but an existing EC key + CertificateRequest to generate the certificate in memory. All unit tests are passing now.

The parameter representAsRsaKey exposed by JsonWebKeyConverter.ConvertFromX509SecurityKey should be renamed as now ECDsa is supported. I'm open to suggestions.

Otherwise, this PR is ready to be reviewed.