For the callback case, testing is quite simple as follows:
Start eXo Platform server and OpenAM Tomcat server.
Open a browser, then browse http://localhost:8080/portal/. You will be redirected to the OpenAM centralized authentication form.
Log in with the eXo Platform credentials (for example, root/gtn). You will be auto-logged in and redirected to the eXo Platform homepage.
In case of non-callback, note again that the user must be registered in both the external datasource and eXo Platform. Also, log in with the credentials created in the external datasource (for example, root/12345678).
In case eXo Platform and OpenAM are deployed into different domains, move to the next section for for more details.