pairing on hci level with pin

Hi all,

I'm currently working on a home project about data transmission over
bluetooth with pin-pairing. I've learned how to get rfcomm-connection
established and work. The pin has to be hard coded in the program,
because it is an embedded system and there won't be a user interaction.

But when I come to implement pairing with pin, what hci_request do I
have to send to get the devices to pair?
Another question that I couldn't resolve is the purpose of the pin_type
variable. What is it for?

Best regards,

Alejandro