Correct AuthenticatorAssertionRawResponse.Id type

[Regenhardt]

The AuthenticatorAssertionRawResponse class has two byte[] members Id and RawId. Both used, although RawId is just checked for existence and in tests.

As per MDN Id is literally the base64url encoded value of RawId, I think Id should rather be a string and not base64url-decoded when received, but kept as string. The places currently using the Id property should use RawId instead.

I just debugged into an assertion, and Id and RawId do indeed have the exact same value in the backend.

[Regenhardt]

Since a major update is planned anyway, would you accept a PR amending that?

[abergs]

@Regenhardt Yeah this is interesting and 4.0 would be a good opportunity to fix this. I do wonder about the implications that this will have though.

[abergs]

@Regenhardt You're welcome to submit a PR and we can further discuss the feasibility