Added URLCredential documentation

README.md

@@ -452,7 +452,7 @@ Even in an age where we trust our portable devices with the most private data, a
 
 ### Data Storage
 
-If your app needs to store sensitive data, such as a username and password, an authentication token or some personal user details, you need to keep these in a location where they cannot be accessed from outside the app. Never use `NSUserDefaults`, other plist files on disk or Core Data for this, as they are not encrypted! In most such cases, the iOS Keychain is your friend. If you're uncomfortable working with the C APIs directly, you can use a wrapper library such as [SSKeychain][sskeychain] or [UICKeyChainStore][uickeychainstore].
+If your app needs to store sensitive data, such as a username and password, an authentication token or some personal user details, you need to keep these in a location where they cannot be accessed from outside the app. Never use `NSUserDefaults`, other plist files on disk or Core Data for this, as they are not encrypted! In most such cases, the iOS Keychain is your friend. It is best to store your credentials in the iOS Keychain with [NSURLCredential](https://developer.apple.com/documentation/foundation/nsurlcredential) and [NSURLCredentialStorage](https://developer.apple.com/documentation/foundation/nsurlcredentialstorage). You create and store your access token in a `NSURLCredential`, and store that credential in a `NSURLCredentialStorage` instance. You will also need to specify a [NSURLProtectionSpace](https://developer.apple.com/documentation/foundation/urlprotectionspace), which represents a server or an area on a server, commonly referred to as a realm, that requires authentication. You can persist the credentials in the user's keychain, or for a single request. There are also wrapper libraries such as [SSKeychain][sskeychain] or [UICKeyChainStore][uickeychainstore], that let you interact with the keychain directly, but this is not recommended.
 
 When storing files and passwords, be sure to set the correct protection level, and choose it conservatively. If you need access while the device is locked (e.g. for background tasks), use the "accessible after first unlock" variety. In other cases, you should probably require that the device is unlocked to access the data. Only keep sensitive data around while you need it.