Useful plugin for restricting website access via token

I wanted to have links on Site A (authorised members only site) to send people to Site B and allow them access to it.
Without unauthorised people being able to go direct to Site B and having access.
OK so a member of Site A could get the most current token and give it to friends but, I’m sure I could run a con job to update the URL token on the private page on Site A and also in the Mysql database on Site B or something.
Good plugin.

Took me a while to find a solution so some keywords to help others find this:
Allow cross domain access to website secure token authorisation