The API to verify a license seems to work with a simple https access which also includes some sensible information (mainly API key) - this does seem to be a bit old school.
Do you plan to improve this to work with encrypted data. For example the license key of a customer can be sent to the API which encrypts it using RSA using the private key. The encrypted key and a time stamp is sent back and the software can check the resonse if it can be decrypted using the public key. If yes, the license is valid for a certain time, therefor the timestamp. The code for this is pretty simple and can be done in PHP.