-Z VerifyClient

The -tlsVerifyClient option is used to define whether a TELNET client requires a certificate to access a server.

-Z VerifyClient

={NONE | OPTIONAL | REQUIRE}

NONE

The TELNET server does not request a certificate from the TELNET client.
NONE is the default.

OPTIONAL

The TELNET server requests the TELNET client to send its certificate. If the client refuses to do this or supplies an invalid certificate, access is nevertheless allowed.

REQUIRE

The TELNET client must transfer a valid certificate, otherwise access is refused.