If you need to display a different success page to your users depending on what authentication provider they use to connect, have a look at this guide.
All you need to do is add a new hidden <input> tag to your authentication provider's form.
1. Navigate to Network -> Captive Portals -> Your Captive Portal -> Authentication providers.
2. Click the edit icon next to the authentication provider's name.
3. Paste the code below just before the ending </form> tag. For example, if we want to redirect the user to www.google.com, the value of the <input> tag will be www.google.com.
<input type="text" name="success_page" id="success_page" value="www.google.com" hidden/>