Install libapache2-mod-gnutls by entering the following commands in the terminal:
sudo apt update sudo apt install libapache2-mod-gnutls
Description:
Apache module for SSL and TLS encryption with GnuTLS
mod_gnutls provides TLS encryption using the GnuTLS library. It's similar in purpose to mod_ssl, but doesn't use OpenSSL, and provides some additional features: * PKCS #11 access to server keys and certificates, * OpenPGP authentication, and * using Monkeysphere for client certificate validation.
Homepage: https://mod.gnutls.org/
Version: 0.8.2-3ubuntu1
Section: universe/web