"blank page" error when setting parameter $rcmail_config['cas_validation']

[thangnguyennang]

Hi dfwarden,

I have an "blank page" issue when accessing CAS server:
https://cas-server-hostname/webmail/?_action=caslogin

CAS server uses self-signed certs and I set correctly the roundcube plugin's parameters:
$rcmail_config['cas_validation'] = 'self';
$rcmail_config['cas_cert'] = 'path-to-certs.pem';

PS. If changing 'self' to 'ca', I can access to CAS server's login page normally.

Any suggestions for me? Thanks in advance.