There may be cases where your main site is not a vBulletin site and you have a forum section using vBulletin 5. And there may be instances where you would want to re-use the vB5 login page then after a successful login, redirect to the main site.

How would you do that? It's easy.

For example, your main site is http://example.com/ and your vB5 forum is http://example.com/forum/
  1. In your main site, you can reference to the vB5 login page inside an iframe or in its own window using the following URL:
    Code:
    http://example.com/forum/auth/login-form?url=aHR0cDovL2V4YW1wbGUuY29tLw==
    You are passing "url" querystring with a value of Base64 encoded URL which is in our example, http://example.com/
    There are Base64 encoder tools online that you can use to do this. One of them is http://www.motobit.com/util/base64-decoder-encoder.asp.
  2. Once vB5 authentication is successful, it decodes the url querystring value and redirects to that URL.
Demo:
Open the link below in Private Mode or Incognito Mode to login to this site (obviously, you need to be a registered user here). Once you successfully logged in, you will be redirected to http://www.vbulletin.com/forum/ and not to this site.

http://vbmods.rocks/auth/login-form?...9tL2ZvcnVtLw==

That's it. Enjoy!