How to validate host keys (i.e. how to access information about `NIOSSHPublicKey`)?

SwiftNIO SSH commit hash: 5d95ebaddd7f546502f9760df3a2de8c167369da

Context:
I'm trying to implement a `NIOSSHClientServerAuthenticationDelegate` that actually verifies the host key.

The problem:
Except for debug printing, I have not found any way to access any information about the supplied `NIOSSHPublicKey`.

Is there currently a way to access information about a `NIOSSHPublicKey`? (Apologies if I missed something obvious, I'm fairly new to swift).

System Information

```sh
$ swift --version
Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)
Target: x86_64-apple-darwin19.6.0

$ uname -a
Darwin tim-mac.local 19.6.0 Darwin Kernel Version 19.6.0: Mon Aug 31 22:12:52 PDT 2020; root:xnu-6153.141.2~1/RELEASE_X86_64 x86_64 i386 MacBookPro12,1 Darwin
```

Start with NIOSSHClientServerAuthenticationDelegate and NIOSSHPublicKey at commit 5d95ebaddd7f546502f9760df3a2de8c167369da, and inspect the public API around the supplied host key. Done means establishing a clear supported way to access key information for host-key verification, with the behavior and limitations documented or covered by tests.

Written by the indexing model from the issue text.