Refactor `ClientCertificateCredential` to use `AadClient`#11719

Merged

chlowell merged 2 commits intoAzure:masterfrom chlowell:certificate-aadclient

Jun 4, 2020

+174-71

Commits on May 29, 2020

AadClient supports authentication by cert
chlowell
committed

Commits on May 30, 2020

CertificateCredential uses AadClient
chlowell
committed