Unfortunately the PIN is a security requirement put in place by Google and it's unlikely they will ever change this requirement. It's so no one can yell "OK Google, unlock my door!" and be able to unlock your door and access your home without authorization. We're currently still waiting on Google to enable 2FA so we can implement unlocking for Sesame as a Google Home Control device.
However, the IFTTT applet doesn't have this restriction/protection in place, and you can unlock the door by saying "OK Google, Open Sesame" if you have the applet turned on. Hope this helps and let us know if you have any further questions! - CANDY HOUSE