@zangdaarr.mortpartou welcome to the community!
Here's a porting guide:
One thing to consider is if the API for the lock is in the cloud you will still be dependent on your internet connection. If you can find a local way of doing it, it will be nicer, but that is not always possible, just as you say.
Developer Documentation is here:
https://docs.hubitat.com/index.php?title=Developer_Documentation
And this is how you install custom drivers:
https://docs.hubitat.com/index.php?title=How_to_Install_Custom_Drivers
EDIT: A quick search gave me this:
https://medium.com/@nolanbrown/august-lock-rest-apis-the-basics-7ec7f31e7874
https://medium.com/@nolanbrown/the-process-of-reverse-engineering-the-august-lock-api-9dbd12ab65cb
The above together with the DTH from ST you should have no problem getting it to work. Polling frequently for status from HE is something that should be avoided, search the forum and you'll find plenty on that subject.
EDIT2: For a 100% offline solution, this could be used:
