to better the user experience, mark a few of the open id connect
options as required, users should get back more meaningful
error messages.
as part of the change, there was also a discrepancy between what
the loader used for the authorization code, and what the plugin
was using. deprecate the old loader option (authorization-code)
in favor of the one used by the plugin (code).
Change-Id: I18318ef44f99e4f973176dd99b61770b1151f7a0
Partial-Bug: 1593192
827895281b