If you have been using the Mac OS for any amount of time then you are likely aware of Apple’s password management system known as the Keychain. iOS devices also have a keychain system for storing user data securely.
If you need to store username/password data for a web service securely within your apps then you will likely want to use the iOS keychain service. I’ve found an excellent guide explaining the basics of reading and writing to the keychain. Also included is a sample project demonstrating keychain usage (you will need to run on an actual device to test real saving/loading to the keychain).
The tutorial on using the keychain to store username and password is no longer up to date and has been removed – please check out this tutorial that explains how to use the iOS keychain and this excellent iOS keychain wrapper.
A nice easy to follow guide in case you ever need to use the Keychain service within your apps.