1. add to vhost entry "SetEnv HTTPS on", example below

<VirtualHost *:443>
    ServerAdmin admin@domain.tld
    DocumentRoot "/www"
    ServerName my.domain.tld
    ServerAlias www.my.domain.tld

     SetEnv HTTPS on
     SSLProtocol all -SSLv2
     SSLCipherSuite HIGH:MEDIUM:!aNULL:!MD5
     SSLCertificateFile "_MY_CERT_"
     SSLCertificateKeyFile "_MY_CERT_"
     SSLCertificateChainFile "_MY_CERT_"

      <Directory /my/dir>
                Options  FollowSymLinks
                AllowOverride All
                Require all granted
       </Directory>
</VirtualHost>

2. edit file configuration.php (joomla root folder)

3. set variable to your domain with htttps prefix,

public $live_site = 'https://my.domain.tld';

4. (optional) change forcing sll variable,

public $force_ssl = '0';  to public $force_ssl = '2';