I used the same setup for openssl from here: https://answers.ros.org/question/198647/rosbridge-websocket-ssl-connection-aborted/

Key:
openssl genrsa -out server_key.pem 2048

Certificate Signing Request:
openssl req -new -key serverkey.pem -out servercsr.pem

Certificate:
openssl x509 -req -days 1825 -in servercsr.pem -signkey serverkey.pem -out server_cert.pem

My launch-file-arguments:

  <arg name="port" default="9090" />  
  <arg name="address" default="" />
  <arg name="ssl" default="true" />
  <arg name="certfile" default="/home/user/ssl/server_cert.pem" />
  <arg name="keyfile" default="/home/user/ssl/server_key.pem" />
  <arg name="authenticate" default="false" />

and can get to the websocket endpoint by going to https://xxx.xxx.x.xxx:9090/

I would like to now be able to connect with the endpoint using webviz.io.
I try to do this be going here: https://webviz.io/app/?rosbridge-websocket-url=https://xxx.xxx.x.xxx:9090

however it never connects... I just get the spinning circle. If I'm on a separate computer (same network) I get the warning about an untrusted certificate and I "agree" to using it, on the same computer I don't get that notice, but still no connection.