If you are going to store the information in the properties, you should be aware that the is information persisted on the device.
The use of properties for short term storage IMHO should be avoided if possible.
You have two choices, one store your variables in the Titanium namespace
Titanium.App.credentials = { "user" :"username", "pwd":"password123"};
Or create your own namespace and store your variable there. This will ensure you values are available throughout the application, but not stored on the device.
There is an example on my blog here http://blog.clearlyinnovative.com/post/6519148138/titanium-appcelerator-quickie-global-variables-scopes