Do you want the application "rapportd" to accept incoming network connections?

Updating a family member's iMac 27" to High Sierra for the first time. After the c. 40-minute update, we went on and proceeded with the set-up and came to the option to set up iCloud. Upon clicking to do so, an alert pane opened up (with the "exclamation point" icon in a yellow triangle) which read:

Do you want the application "rapportd" to accept incoming network connections?

Clicking Deny may limit the application's behavior. This setting can be changed in the Firewall pane of Security & Privacy preferences.

Deny / Allow

I read a 3-page thread where others asking a similar question were responded to with some speculation, but I'm not sure that there was an official answer as to what the "rapportd" app is, what purpose it serves, and how its "behavior" would be affected by denying or allowing it to accept incoming network connections.

Thanks,

J