I think that add_auth_errors ignores the authenticate_args hash, because it looks like:
sub add_auth_errors {
my $self = shift;
$self->field( 'password' )->add_error( $self->login_error_message )
if $self->field( 'username' )->has_value && $self->field( 'password' )->has_value;
}
So it seems to ignore if the user changes the authenticate_username_field_name or authenticate_password_field_name. Also