facebook social game signup and logon design

Question

Hi,

we are migrating an existing multiplayer game to be a facebook oriented. the game has flex client side, .NET server and a WCF comunication.

I'm currently checking the follwing tasks:

1. FacebookSignUp() method: I would like to create a facebook specific signup() for all facebook users. this method should automatically generate a new user based on its facebook profile information.

2. FacebookLogon() since facebook users will not have password, we will create specific logon method for facebook users according their facebook logon status.

3. server side(.NET): should be able to post wall messages of the facebook user

4. client side(flex): should enable the users to manually invite their friends to the game.

our main concert is with the signup and the logon implementation: how can I ensure that the users can not steel other users' identities?

another issue is the application secret - how can keep the application secert confident while enabling the flex client exeute operations agains facebook?

I'll be happy to hear any design comments regarding those (I guess simple..) tasks.

ofer