algrid

    static func loadBioProtected(key: String, context: LAContext? = nil,
                                 prompt: String? = nil) -> Data? {
        var query: [String: Any] = [
            kSecClass as String       : kSecClassGenericPassword,
            kSecAttrAccount as String : key,
            kSecReturnData as String  : kCFBooleanTrue,
            kSecAttrAccessControl as String: getBioSecAccessControl(),
            kSecMatchLimit as String  : kSecMatchLimitOne ]
        
        if let context = context {

algrid

    checkBiometryState { success in
        guard success else {
            // Biometric authentication is not available
            return
        }
        DispatchQueue.global().async {
            var result = ""
            if let data = KeychainHelper.loadBioProtected(key: self.entryName,
                                                          prompt: "Access sample keychain entry") {
                let dataStr = String(decoding: data, as: UTF8.self)

algrid

    private func checkBiometryState(_ completion: @escaping (Bool)->Void) {
        let bioState = self.biometryState
        guard bioState != .notAvailable else {
            // Can't read entry, biometry not available
            completion(false)
            return
        }
        if bioState == .locked {
            // To unlock biometric authentication iOS requires user to enter a valid passcode
            let authContext = LAContext()

algrid

    static func getBioSecAccessControl() -> SecAccessControl {
        var access: SecAccessControl?
        var error: Unmanaged<CFError>?
        
        if #available(iOS 11.3, *) {
            access = SecAccessControlCreateWithFlags(nil,
                kSecAttrAccessibleWhenUnlockedThisDeviceOnly,
                .biometryCurrentSet,
                &error)
        } else {

algrid

    enum BiometryState {
        case available, locked, notAvailable
    }

    var biometryState: BiometryState {
        let authContext = LAContext()
        var error: NSError?
        
        let biometryAvailable = authContext.canEvaluatePolicy(
            LAPolicy.deviceOwnerAuthenticationWithBiometrics, error: &error)

algrid

    let context = LAContext()
    let password = pwTextField.text ?? ""
    context.setCredential(Data(password.utf8), type: .applicationPassword)
    let data = KeychainHelper.loadPassProtected(key: self.entryName, context: context)
    // Update UI for data

algrid

    let context = LAContext()
    let accessControl = KeychainHelper.getPwSecAccessControl()
    context.evaluateAccessControl(accessControl, operation: .useItem, localizedReason: "Not used") { (success, error) in
        DispatchQueue.main.async {
            guard success else {
                self.showStatus("evaluateAccessControl failed: \(error?.localizedDescription ?? "no error")")
                return
            }
            let data = KeychainHelper.loadPassProtected(key: self.entryName, context: context)
            // Update UI for data

algrid

    DispatchQueue.global().async {
        let data = KeychainHelper.loadPassProtected(key: self.entryName)
        DispatchQueue.main.async {
            // Update UI for data
        }
    }

algrid

    static func loadPassProtected(key: String, context: LAContext? = nil) -> Data? {
        var query: [String: Any] = [
            kSecClass as String       : kSecClassGenericPassword,
            kSecAttrAccount as String : key,
            kSecReturnData as String  : kCFBooleanTrue,
            kSecAttrAccessControl as String: getPwSecAccessControl(),
            kSecMatchLimit as String  : kSecMatchLimitOne]
        
        if let context = context {
            query[kSecUseAuthenticationContext as String] = context

algrid

    static func getPwSecAccessControl() -> SecAccessControl {
        var access: SecAccessControl?
        var error: Unmanaged<CFError>?
        
        access = SecAccessControlCreateWithFlags(nil,
            kSecAttrAccessibleWhenUnlockedThisDeviceOnly,
            .applicationPassword,
            &error)
        precondition(access != nil, "SecAccessControlCreateWithFlags failed")
        return access!