Store unused OIDC arguments
    
    Store arguments that we do not support yet but that clients provide us
    with, so that when we do support them in the future, we have not thrown
    the information away.
    
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>