I am trying to figure out how to go about enabling the short term key pass code method between two devices. every promising link to this website leads to a broken or dead link.
MbedOS 6.15 has been with us for a good while now so any link using 6.15 should be working.
You can use the SecurityManager header file, as noted in the Mbed BLE API.
Here is the link in GitHub as there is no additional documentation other than the detailed comments provided in this header file: mbed-os/SecurityManager.h at master · ARMmbed/mbed-os · GitHub
Search for “Sequence diagram for Secure Connections passkey entry pairing”
This describes the process involved.