Aqui está como eu implementei isso (xxx.xxx.xxx.xxx - permitir acesso para este endereço sem cert):
SSLVerifyClient optional
SSLOptions -FakeBasicAuth +StrictRequire -StdEnvVars -ExportCertData
SSLRequire %{SSL_CIPHER_USEKEYSIZE} >= 128
RewriteEngine on
RewriteCond %{SSL:SSL_CLIENT_VERIFY} !^SUCCESS$
RewriteCond %{REMOTE_ADDR} !^xxx.xxx.xxx.xxx$
RewriteRule ^ - [F]
Observe que o SSLVerifyClient NÃO deve estar no contexto do diretório:
In per-directory context it forces a SSL renegotiation with the reconfigured client verification level after the HTTP request was read but before the HTTP response is sent.