client does not have to send one, with the B<-Verify> option the client
must supply a certificate or an error occurs.
+If the ciphersuite cannot request a client certificate (for example an
+anonymous ciphersuite or PSK) this option has no effect.
+
=item B<-crl_check>, B<-crl_check_all>
Check the peer certificate has not been revoked by its CA.