Rename the short for the OAuth2 AuthMethod, remove ar from the authcontroller methods, and add grant as an argument to authenticate.

Signed-off-by: Tyler O'Meara <Tyler@TylerOMeara.com>
Refactor the legacy Core auth method to use the AuthorizationMethod class.

Signed-off-by: Tyler O'Meara <Tyler@TylerOMeara.com>