ASMScaleUser needs to implement NSObject, too.
Add a facility to retrieve the appropriate service provider for a given scale user.
Start adding support for storing an oauth 1 token in the keychain
To get things up and running quickly, use FXKeychain to interact with the keychain.
Create an API to store and retrieve OAuth 1 access tokens in the keychain.
Add API to the scale user protocol to check whether the user is authenticated and to store and retrieve sensitive information in the keychain. Implement this for Withings users.
Create Withings user from response from getbyuserid call. Also, the Withings service provider should not hold the access token since it is user-specific.