Get device info from header

Hi,
I have a node.js back end with a mobile (ios and android) and web front end.
It is accessed but a limited number of my clients existing customers and he has asked for some logging of who is using what device to access he system.
I know I can use the browser component to get information and send that back with post etc. but since some info is returned with api calls already (in the header?), is there a way to access this data in the backend to save to a log table?
Thanks.