Since 13:06 UTC, Connect cPanel/WHM has a second way in: I'm a WHM reseller (no root). A reseller whose hosting provider has given them the List Accounts and Manage API Tokens privileges creates their own WHM token with only List Accounts, restricted to the server's own addresses, and pastes our commands into their cPanel account's shell. The token stays in their account on the server and is never sent to us; a script in their crontab reports the accounts they own every ten minutes, and if any account's answer is missing the whole report is rejected, so a partial list never pauses sites. Server owners with root keep the existing flow.
The integration now has its own page, cPanel/WHM uptime monitoring, and the steps are in the docs.