Public certificate authentication is not available on Fuse 6.x after fabric creation

Issue

Fuse 6.x exposes a command-line administration interface using the supplied client utility, or simply by connecting any SSH client to the console port, typically 8101. This interface supports user-password authentication, and also public certificate authentication using an RSA public key, as documented here.

After creating or joining a fabric, however (fabric:create or fabric:join) this procedure no longer works. The authentication will simply fail, with no particular error message.