What is rapportd and why does it want incoming network connections?

I've just updated to the latest MacOS 10.13.2 and after restarting, my machine asked me to allow incoming network connections for "rapportd". After blocking it and checking in the firewall config, I can see that this is an executable in /usr/libexec/rapportd which was created on my machine on the 1st of December. That's a day after I installed the security update 2017-001 (for the second time; autoupdate didn't seem to notice that I'd manually updated it), and I haven't installed or updated any other software recently / around that time. Google Chrome updates whenever it feels like it, so this could be related to a Chrome update (no idea when it last updated). The internet suggests this is related to some banking protection program but that doesn't seem to fit here, and from a vague text-edit inspection of the binary I can see that it references /System/Library/PrivateFrameworks/Rapport.framework/Versions/A/Rapport (a framework created on my machine back in July and updated in October) which makes me think this is likely to be a new 1st-party OS daemon. --- What does rapportd do?