I believe this will do the trick, as far as what the docs imply

(def-key ::ring-handler      ::string-or-named

  "If you want to embed a ring handler into the figwheel http-kit server;
this is for simple ring servers, if this doesn't work for you just run
your own server.
Default: Off
  :ring-handler example.core/my-server-handler")

I'm more of a pedestal fan myself, but it appears dropping in https://github.com/r0man/ring-cors should handle it

You should see the browser make an options request to get the CORS settings ... I'd just set the allow-origin to *