How to receive JSON payload from a digital device

I have a site with about 100 registered users. Some of the people will be receiving digital scales. The scales send their weight data to a 3rd party server that then sends a JSON Payload as an HTTP Post to a URL endpoint (my server). The message can include Basic authentication. Can anyone recommend the best approach to get the data into the WP database. Initially I just want to add the weight to their profile with user_metadata. Eventually I will process the dat more. I’m good with WordPress but can’t figure out how to jump from http post into wp or even just mysql.