Example: SSLVerifyClient require
Since: Apache 1.3
This directive sets the certificate verification type for
client authentication. Notice that it can be
used in either per-server or per-directory context. In per-server
context, it applies to the client authentication process used in
the standard SSL handshake when a connection is established.
In per-directory context, it forces an SSL renegotiation with the
reconfigured client verification level after the HTTP request
is read but before the HTTP response is sent.
The following type variants are possible: ``none'' where
no client certificate is required; ``optional'' where
the client may present a valid certificate; ``require''
where the client must to present a valid certificate; and
``optional_no_ca'' where the client may present a valid
certificate but has not to be (successfully) verifiable.