Add support for DNS in non-Windows environments

[SteveSyfuhs]

Is your feature request related to a problem? Please describe. DNS lookups only work on Windows today because it calls into win32 APIs directly. .NET doesn't provide a way to query for SRV records.

Describe the solution you'd like The library needs a way to make DNS queries outside of Windows. The solution should be to provide a way to bring your own DNS implementation that way you can use something like https://github.com/MichaCo/DnsClient.NET on other platforms.

Describe alternatives you've considered You could rely completely on a krb5 configuration file to provide all the necessary records, but that's complicated and messy.

Additional context Design should be similar to the CryptoPal so callers can register their DNS mechanisms. A side-car nuget package could be created that wires in the DnsClient.NET implementation.

[SteveSyfuhs]

For folks running into this issue, there's a super simple platform-independent implementation available in the Bruce tool. It uses the DnsClient.NET library as mentioned above. It's kept out of the main project reduce total external dependencies.

https://github.com/dotnet/Kerberos.NET/blob/946daea47a347a0ad9dcb645f2c6e82a8c94372f/Bruce/Dns/PlatformIndependentDnsClient.cs#L1-L50

[MageFroh]

This class is very useful, but a bit hard to find. Is there a NuGet package that includes it? Would be great to be able to include something like Kerberos.NET.Portable, instead of copying the class in all projects that need it.

[SteveSyfuhs]

PR's are accepted to get that working.

[0x5ECF4ULT]

As requested by the contribution guidelines: I'm working on it

[SteveSyfuhs]

Awesome! The build process is somewhat of a pain to verify, but it should just be a matter of duplicating the kerberos.net lines in the build file and replacing the names with the new project/package name (https://github.com/dotnet/Kerberos.NET/blob/develop/build.yaml)