Pass validated client credential to AuthorizationHandler

[tsuyoshizawa]

fix #113

We removed AuthorizationHandler#clientCredential by #110

But AuthorizationHandler#validateClient and AuthorizationHandler#findUser may use it.
We needed to pass validated client credential to it.

[rmmeans]

This looks good to me 👍 and makes it easier. I understand the problem in #113, but you could work-around it just like before and ask parse the client credential (what we are doing right now) - but then they have to deal with the Either[InvalidClient, ClientCredential] type which is not as nice. This will make it simpler to deal with it at the data handler layer.

[tsuyoshizawa]

Thank you for review.

but they have to deal with the Either[InvalidClient, ClientCredential] type which is not as nice

Yes, I agree with you. InvalidClient is already validated before executing validateClient and findUser in AuthorizationHandler. We need just Option[ClientCredential].

I will merge and release.
Thank you again.