Add EdDSA algorithm support

[lritter14]

Allows for providers to use EdDSA algorithm but does not support verifying access tokens.

[ericchiang]

Out of curiosity, what providers support this?

Would it be possible to add some tests that actually exercise the signing and verification? E.g. take a look at jwks_test.go verify_test.go

If not, I can take a crack at it

[ericchiang]

wouldn't this be sha512.New()?

[lritter14]

I believe that verifying EdDSA key with ed25519 protocol is a bit more complicated than the pattern that exists here short explanation

[ericchiang]

This is only for the at_hash value, it's not doing full verification :)

[lritter14]

Out of curiosity, what providers support this?

Would it be possible to add some tests that actually exercise the signing and verification? E.g. take a look at jwks_test.go verify_test.go

If not, I can take a crack at it

Here is an example provider that supports EdDSA. I was not originally planning on adding verification functionality as it is more complicated for ed25519 protocol.

[ericchiang]

Did you mean to hyperlink something in that comment?

I don't think I'd want to merge this if it only implements partial support. I can add verification functionality when I get a sec.

[lritter14]

I added some additional tests and took your suggestion for using sha512.New() to verify the hash. I am not super knowledgeable in this space so I am not confident in that change.

P.S. closing the PR was a mistake

[ericchiang]

Awesome, thanks for sending the full change. Lgtm :)

[ericchiang]

If there are any issues with the at_hash support, we can always fix it up later. I'm not super worried about it.