When using MAC OS Mountain Lion, it uses User-Agent: ocspd/1.0 to verify certificate validity, the user agent is not able to authenticate and needs to be bypassed in the authentication layer.
Authentication can be bypassed in CPL or VPM as described below.
To bypass this user agent, the following CPL can be used
In VPM, create a new rule in the top of your authentication layer
where the Source is defined with ocspd/1.0, as in the screenshot below.