How to add a extension to guacamole?

I want to add an extension to guacamole. The Problem is first of all that there are two docker containers for guacamole and I don’t know in which one I should put the “.jar” file because I want to add the TOTP extension. In both containers, there isn’t the default GUACAMOLE_HOME path, normally under /etc/guacamole. There is only in the container “guacamole_guacamole_1” a path to /opt/guacamole with some folders, but if I create an extension folder with the .jar inside it doesn’t work and there is no error. It would be great if there is any easy way to add extensions.

Thank you for your help