Enable ssl by typing this command sudo a2enmod ssl

Enabling ssl requires the apache2 service should be restarted, so restart apache by using this command service apache2 restart

Create a directory for the Self-Signed certificate by using sudo mkdir /etc/ssl

Generate Self-Signed Certificate by using the below command

       sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048  - keyout  /etc/ssl/client.key -out /etc/ssl/client.crt 

         The above command generates client.key file and client.crt file

Convert the generated files into pem format by using follwing commands

         cat client.key > /etc/ssl/client-key.pem 

         cat client.crt > /etc/ssl/client-cert.pem

Combine the client-key.pem and client-cert.pem by using this command cat client-key.pem client-cert.pem > client.pem

The client-key.pem is the keyfile and the client.pem is the certificate file for Self- signed certificate

Configuring SSL in /etc/apache2/sites-available/default-ssl.conf

 <IfModule mod_ssl.c>
         <VirtualHost _default_:443>
                 ServerAdmin your_email@example.com
                 ServerName server_domain_or_IP

                 DocumentRoot /var/www/html

                 ErrorLog ${APACHE_LOG_DIR}/error.log
                 CustomLog ${APACHE_LOG_DIR}/access.log combined

                 SSLEngine on

                 SSLCertificateFile       /etc/ssl/client.pem 
                 SSLCertificateKeyFile  /etc/ssl/client-key.pem 

                 <FilesMatch "\.(cgi|shtml|phtml|php)$">
                                 SSLOptions +StdEnvVars
                 </FilesMatch>
                 <Directory /usr/lib/cgi-bin>
                                 SSLOptions +StdEnvVars
                 </Directory>

                 BrowserMatch "MSIE [2-6]" \
                                nokeepalive ssl-unclean-shutdown \
                                downgrade-1.0 force-response-1.0

         </VirtualHost>  </IfModule>

After making these changes, your server block should look similar to this: