An input device includes an input-sensing unit that contains a capacitive input sensor and a sensitivity-sensing unit that contains a capacitive sensitivity sensor. A certificate validation service receives a certificate validation request for a target certificate from a client, thereby allowing the client to offload certificate validation tasks into an online certificate validation service that is accessible and sharable by multiple components within a data processing system. If the received user gesture matches one of the authorized user gestures, the example method include granting access to the computing device andor a user account.