mod_sslcrl is a module for the Apache Web server. It verifies the validity of client certificates againts Certificate Revocation Lists (CRL) of Certification Authorities (CA). It may be used in conjunction with mod_ssl when x509 client certificate authentication is used. mod_sslcrl replaces the mod_ssl directives SSLCARevocationFile and SSLCARevocationPath automatically downloading CRL files from CAs via HTTP(S).