Add OAuth Authorization Code Flow suppport

"To access the Quay API I need to create an application. This app only supports the OAuth implicit flow which is kind of outdated. In the quay.io docs even the referenced Google document (https://docs.quay.io/api/) describes the OAuth Authorization Code Flow (https://developers.google.com/identity/protocols/oauth2/web-server).
The missing support of OAuth Authorization Code Flow prevents us of integrating Quay with other Applications. Therefore It should be supported."