This is the first article in a six-part series about Keychain on iOS. It starts with how Keychain is structured, then covers accessibility classes and how to choose between them. The article notes that a token in an app is almost always first put in UserDefaults and later moved to Keychain, usually following an example from the internet. Such examples often say nothing about kSecAttrAccessible, an attribute that determines when a record can be read at all.