Hi Raphael, you can edit the server.xml in the Tomcat \conf directory if you’re hosting DHIS directly on Tomcat. If you use a reverse proxy, you would need to set that up accordingly. See the installation chapter of the administrators manual here: https://docs.dhis2.org/2.34/en/dhis2_system_administration_guide/installation.html
Look for the Tomcat installation section.
What is your environment?
What server operating system are you running?
Are you Running Tomcat + PostgreSQL or do you also have a reverse proxy (nginx or apache)?
For TLS (https) you need a server certificate and key. There are different ways to get one with the ideal way being to purchase a certificate from a provider such as godaddy or comodo, but you can also use a free certificate service such as letsencrypt which requires you to renew the certificate regularly (every 3 months). The effort required and instructions depend on your environment, so let us know more and we’ll try to help.