Read certificates as PEM strings or from files

[mtmk]

No description provided.

[caleblloyd]

What do you think about offering a couple of callbacks instead? Then some static methods to help configure the callbacks for common cases? I can see many more requests in this area on the horizon - PFX certificates, private keys with passwords, etc

public sealed record NatsTlsOpts {
    public Func<ValueTask<X509Certificate2>>? LoadClientCert { get; init; }

    public Func<ValueTask<X509Certificate2Collection>>? LoadCaCerts { get; init; }

    public static Func<ValueTask<X509Certificate2>> LoadClientCertFromPemString(string certPem, string keyPem)
    {
        var clientCert = X509Certificate2.CreateFromPem(certPem, keyPem);
        return () => ValueTask.FromResult(clientCert);
    }

    public static Func<ValueTask<X509Certificate2Collection>> LoadCaCertsFromPemString(string caPem)
    {
        var caCerts = new X509Certificate2Collection();
        caCerts.ImportFromPem(caPem);
        return () => ValueTask.FromResult(caCerts);
    }
}

Note that this is not a full replacement for LocalCertificateSelectionCallback and RemoteCertificateValidationCallback - it's just a way to load other X509 Certificates and use them with our default LocalCertificateSelectionCallback and RemoteCertificateValidationCallback implementations. I can also see being asked to provide overrides for LocalCertificateSelectionCallback and RemoteCertificateValidationCallback in the future, but of course we can address that later.

[mtmk]

@caleblloyd why don't you just hack it into the branch? Not sure exactly what you mean.

[caleblloyd]

Sure, will open a PR to this one

[caleblloyd]

LGTM