Where is the document about the format info of "ca-certs-file" ???

[Leon Ann]

I'm trying to build a Cluster by means of the auto installer.
But I encounter a problem when input the information of remote hosts those are controllable through a standard ssh protocol.
In MySQL Cluster Manual, the description about the "--ca-certs-file" command-line option of the ndb_setup.py is like this:"Specify a file containing a list of client certificates which are allowed to connect to the server. The default is an empty string, which means that no client authentication is used".

But how do i know the format/structure of this file ?
I guess this file should at least contain three aspects information about each remote ssh host:
1.name/ip of remote host;
2.username of remote host;
3.certificate of remote host.
I don't know the format of this file, so I can't construct a one.
Is there any sample/example file in anywhere ?

thanks!