subscription-manager attach - incorrect error message

Just tried to attach a machine for the first time to my developer account.

I was seeing this error in /var/log/rhsm/rhsm.log:
RestlibException: HTTP error (401 - Unauthorized): Unable to make a connection using SSL client certificate.Please review proxy configuration and connectivity.

The actual problem was hidden, which I showed by editing /usr/lib64/python2.7/site-packages/rhsm/connection.py (around line 685) to output more:

{"displayMessage":"You must first accept Red Hat's Terms and conditions. Please visit https://www.redhat.com/wapps/tnc/ackrequired?site=candlepin&event=attachSubscription","requestUuid":"8a458d3b-5edb-4889-8078-13c3cb7ac1fb"}