This article explains how to create a new Twitter custom App and obtain the right permissions to use it.
How to create a new Twitter APP
STEP 1
Go to the registration page and login:
http://dev.twitter.com/apps/new
STEP 2
Click on "Create an app" button and fiil in the required fields.
https://YOURDOMAIN
https://YOUROMAIN/index.php
replacing YOURDOMAIN with your current white label domain (i.e. splash.mydomain.com)
Caution
Make sure there is no whitespace before or after the urls entered, to avoid warning like "Not a valid URL format"

STEP 3
At the end click on "Create " button and read "Review our Developer Terms" then click on Create again

STEP 4
Access to Keys and access Tokens tab to find the Consumer Key (API key) and Consumer Secret (API secret) of your custom application

STEP 5
In order to use the new Twitter App with your own White Label Splash Page, write the API key and API Secret in White Label Splash Editor.
Related Article:
How to configure the Tanaza Splash Page to work with your custom app