gistfile1.js

<fb:login-button onlogin="ask_for_publish_stream_permission();"></fb:login-button>

function ask_for_publish_stream_permission(){
  facebook_prompt_permission('publish_stream', function(accepted) {
    if(accepted) {
      /* Call TA to create/login the fb user */
      new Ajax.Request('/fb_connect/create_user',
      {
         method:'post',
         parameters: {
           facebook_uid: FB.Facebook.apiClient.get_session().uid
         },
        onSuccess: function(data){
          var response = data.responseText;
          if(response == "Success"){
            ajax_login_trigger = document.createElement('a');
            ajax_login_trigger.href = "/fb_connect/link_accounts";
            var valid = new lightbox(ajax_login_trigger);
            valid.activate();
          }
        },
        onFailure: function(){ alert('Something went wrong...') }
      });
    }
    else {
      /* If user has already installed the application but didn't give the extended permissions */
      /* Should we still log them in? */
    }
  });
}

function facebook_prompt_permission(permission, callbackFunc) {
    //check is user already granted for this permission or not
    FB.Facebook.apiClient.users_hasAppPermission(permission,
     function(result) {
        // prompt offline permission
        if (result == 0) {
            // render the permission dialog
            FB.Connect.showPermissionDialog(permission, callbackFunc);
        } else {
            // permission already granted.
            callbackFunc(true);
        }
  });
}