network link user authentication

[KJ]

I have a php script deployed in Apache dynamically generating a kml
file and a network link in GE to pull the latest kml file every 5
minutes. Is it possible to set up user authentication in the following
way:

1) User needs to authenticate with userid/password after he adds the
network link - 1st refresh
2) The subsequent auto-refreshes don't require user authentication -
no manual intervention.
3) After a timeout period, the user is required to authenticate again.