I have tried to add:
        org.keycloak.representations.IDToken idToken = principal.getKeycloakSecurityContext().getIdToken();
        org.keycloak.representations.AccessToken token = principal.getKeycloakSecurityContext().getToken();

        writer.write("<br/>Access Token id: " + token.getId());
        writer.write("<br/>Access Token String: " + principal.getKeycloakSecurityContext().getTokenString());
        writer.write("<br/>ID Token id: " + idToken.getId());
        writer.write("<br/>ID Token String: " + principal.getKeycloakSecurityContext().getIdTokenString());

        writer.write(String.format("<br/><a href=\"/multitenant/%s/logout\">Logout</a>", realm));

        try
        {
                java.net.URL url = new java.net.URL( "http://localhost:8080/auth/admin/realms/" + principal.getKeycloakSecurityContext().getRealm() + "/roles" );
                java.net.HttpURLConnection conn = (java.net.HttpURLConnection)url.openConnection();
                conn.setRequestMethod( "GET" );
                conn.setRequestProperty("Authorization", "Bearer " + principal.getKeycloakSecurityContext().getTokenString());
                java.io.BufferedReader in = new java.io.BufferedReader( new java.io.InputStreamReader( conn.getInputStream()));
                String line;
                while ((line = in.readLine()) != null)
                {
                    writer.write( line );
                }
                in.close();
        }
        catch( Exception e )
        {
                e.printStackTrace();
        }