What is considered best practice to generate a URL that is publicly accessible, but shared via a side channel, so that it is in practice private to the group sharing it?
Something like:
http://example.com/club/XX-XX-XX-XX
http://example.com/club/YY-YY-YY-YY
Where XX-XX-XX-XX shared among one group, and YY-YY-YY-YY is shared by another group. If you have one valid code, it should not be easy to guess other valid codes.
No other security is required for the URL.