Multiple webservices, maintaining authentication?

Hi,
I have multiple webservices which basically look like this -


Auth(uid, pass)
GetData(param1, param2)
GetData2(param1, param2)
..
I don't want unauthenticated access to the GetData methods. So do I just authenticate each time GetData is called? Or is there a better way of doing this?

Thanks,
Teja.
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