The HTTPS protocol can be used as well as the HTTP protocol to fetch resources such as VoiceXML and CCXML applications and any audio or grammar resources that they reference. In this case the truststore used by BVR must be set to trust the certificate provided by the web server hosting those resources. If the required CA is not present in the truststore then it can be added as described here Adding a Certificate Authority to a Truststore (or Keystore).
HTTPS support for resource fetching is available by default and requires no configuration to control its operation.
How to set up a keystore is described here Setting up a Keystore.
How to get a CA signed certificate is described here Getting a certificate signed by a Certificate Authority.