keychain_add.swift

// Lo que vamos a añadir al Keychain...
let query: [String: Any] = [
	kSecClass as String: kSecClassGenericPassword,
	kSecAttrService as String: self.serviceName,
	kSecAttrAccount as String: user.name,
	kSecValueData as String: passwordData
]

// Operación 
let status = SecItemAdd(query as CFDictionary, nil)

// Comprobamos el resultado
if status != errSecSuccess
{
	throw KeychainError.unknown(status: status)
}