implement --ssl-fp and --ssl-fplist for all clients.
--ssl-fp takes one certificate fingerprint, for example,
00:11:22:33:44:55:66:77:88:99:AA:BB:CC:DD:EE:FF:00:11:22:33

--ssl-fplist takes a path to a file with one fingerprint per line.

if the server's certificate fingerprint matches ssl-fp or is found
in the file - the certificate is considered verified.
If the fingerprint is specified but doesn't match - the connection
is aborted independently from the --ssl-verify-server-cert