Apache Reference: mod_ssl, SSLRequireSSL

SSLRequireSSL

Deny Access When SSL Is Not Used for the HTTP Request
Syntax: SSLRequireSSL
Example: SSLRequireSSL
Since: Apache 1.3

This directive forbids access unless HTTP over SSL (that is HTTPS) is enabled for the current connection. It is very handy inside the SSL-enabled virtual host or directories as a defense against configuration errors that expose data that should be protected. When this directive is present, all requests that do not use SSL are denied.