Method to check for validation of a CB user

Hi,
New to joomla (and CB).
Have looked for days for what I suspect is a simple answer.
Hoping someone on the forum can assist!!
We are building a Droid & iPhone app(s) that has a local DB that we would like to synchronize with a server DB.
The user will have a Joomla / CB userID & Password. The user will belong to a community (CB). User's of that community should be able to share this smartPhone / server synchronized data. They should also be able to see that data after logging into CB on the web.

For the basics, we are thinking we need to know if a simple call to the Joomla server:
Validate.php?user=David&passw=Password
can return a simple true/false or such, not an actual login or anything else.

We have tried but there seems to be some Joomla security measures that prevent keeping it that simple. What is the proper way?

For the rest of the solution...we can't be the only CB developers (in training) doing similar...can anyone point us to an existing solution that we could learn joomla / CB methods that accomplish these goals?

TIA

CB has nothing of the sort, you'd need to develop some sort of CB plugin or extension that utilizes CB API to validate the user and accept GET/POST requests. You may want to check Joomla.org extension directory as I'm positive there are numerous mobile solutions and likely something you're wanting already exists. It doesn't need to be CB compatible as all you're trying to do is ensure the Joomla user exists.