This PHP class allows you to authenticate a Yubikey to Yubico's web service API.

Sanitation of the input otp is performed to check for proper length and modhex characters before query is sent to Yubico.

This class fully implements SSL, including verifying the server's certificate domain, expiration date and signing authority. There is also support for signing queries and verifying response signatures.

Timestamp verification is performed with user configurable tolerances to account for clock drift. Both the timestamp tolerances and CURL timeout are readable and writable through accessor methods.