I am working on a java web app, that I will deploy on a tomcat 10 server, which requests a (smart card) certificate from a user to authenticate them (after having entered their regular user credentials). (See also this question that describes more about it.) By setting up the right tomcat server configuration, I have made my web app connect over https (on port 8443). Then, when needed, it will make an https request on another port (8444) to request the user’s certificate.