clear value in keychain when user logout - ios

Question

I want to remove keychain value form my service, when user has logout. However, I feel confused about the best practice way to do that.
Here is my service
let userAccount = "AuthenticatedUser"
let accessGroup = "SecuritySerivice"
let passwordKey = "KeyForPassword"
let kSecClassValue = NSString(format: kSecClass)
let kSecAttrAccountValue = NSString(format: kSecAttrAccount)
let kSecValueDataValue = NSString(format: kSecValueData)
let kSecClassGenericPasswordValue = NSString(format: kSecClassGenericPassword)
let kSecAttrServiceValue = NSString(format: kSecAttrService)
let kSecMatchLimitValue = NSString(format: kSecMatchLimit)
let kSecReturnDataValue = NSString(format: kSecReturnData)
let kSecMatchLimitOneValue = NSString(format: kSecMatchLimitOne)
public class KeychainService: NSObject {
public class func savePassword(token: String) {
self.save(service: passwordKey, data: token)
}
public class func loadPassword() -> String? {
return self.load(service: passwordKey)
}
public class func removePassword() {
}
private class func save(service: String, data: String) {
let dataFromString: Data = data.data(using: String.Encoding(rawValue: String.Encoding.utf8.rawValue), allowLossyConversion: false)!
let keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, userAccount, dataFromString], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecValueDataValue])
SecItemDelete(keychainQuery as CFDictionary)
SecItemAdd(keychainQuery as CFDictionary, nil)
}
private class func load(service: String) -> String? {
let keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, userAccount, kCFBooleanTrue, kSecMatchLimitOneValue], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecReturnDataValue, kSecMatchLimitValue])
var dataTypeRef :AnyObject?
// Search for the keychain items
let status: OSStatus = SecItemCopyMatching(keychainQuery, &dataTypeRef)
var contentsOfKeychain: String? = nil
if status == errSecSuccess {
if let retrievedData = dataTypeRef as? Data {
contentsOfKeychain = String(data: retrievedData, encoding: String.Encoding.utf8)
}
} else {
print("KEY: Nothing was retrieved from the keychain. Status code \(status)")
}
return contentsOfKeychain
}
private class func remove(service: String) {
}
}
Obviously, I'm not shure whether I should remove anything form keychain actually

Answer 1

If you want to delete the item using KeychainItemWrapper, use -resetKeychainItem. This calls SecItemDelete() with the correct value.

Answer 2

To remove username password in Keychain use
func removeUserFromKeychain() {
let spec: NSDictionary = [kSecClass: kSecClassGenericPassword]
SecItemDelete(spec)
}

Answer 3

You can clear your data. Please try below lines
keychain["yourKey"] = nil
or
do {
try keychain.remove("yourKey")
} catch let error {
print("error: \(error)")
}
Thanks