Swift simple keychain helper class for iOS and macOs

KeychainHelper.swift

// MIT License
//
// Copyright (c) 2023 Lee Kah Seng
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

import Foundation

final class KeychainHelper {
    
    static let standard = KeychainHelper()
    private init() {}
    
    func save(_ data: Data, service: String, account: String) {

        let query = [
            kSecValueData: data,
            kSecAttrService: service,
            kSecAttrAccount: account,
            kSecClass: kSecClassGenericPassword
        ] as CFDictionary

        // Add data in query to keychain
        let status = SecItemAdd(query, nil)

        if status == errSecDuplicateItem {
            // Item already exist, thus update it.
            let query = [
                kSecAttrService: service,
                kSecAttrAccount: account,
                kSecClass: kSecClassGenericPassword,
            ] as CFDictionary

            let attributesToUpdate = [kSecValueData: data] as CFDictionary

            // Update existing item
            SecItemUpdate(query, attributesToUpdate)
        }
    }
    
    func read(service: String, account: String) -> Data? {
        
        let query = [
            kSecAttrService: service,
            kSecAttrAccount: account,
            kSecClass: kSecClassGenericPassword,
            kSecReturnData: true
        ] as CFDictionary
        
        var result: AnyObject?
        SecItemCopyMatching(query, &result)
        
        return (result as? Data)
    }
    
    func delete(service: String, account: String) {
        
        let query = [
            kSecAttrService: service,
            kSecAttrAccount: account,
            kSecClass: kSecClassGenericPassword,
            ] as CFDictionary
        
        // Delete item from keychain
        SecItemDelete(query)
    }
}

extension KeychainHelper {
    
    func save<T>(_ item: T, service: String, account: String) where T : Codable {
        
        do {
            // Encode as JSON data and save in keychain
            let data = try JSONEncoder().encode(item)
            save(data, service: service, account: account)
            
        } catch {
            assertionFailure("Fail to encode item for keychain: \(error)")
        }
    }
    
    func read<T>(service: String, account: String, type: T.Type) -> T? where T : Codable {
        
        // Read item data from keychain
        guard let data = read(service: service, account: account) else {
            return nil
        }
        
        // Decode JSON data to object
        do {
            let item = try JSONDecoder().decode(type, from: data)
            return item
        } catch {
            assertionFailure("Fail to decode item for keychain: \(error)")
            return nil
        }
    }
    
}

Hi @LeeKahSeng, thanks for the example and the write-up. Could you please pick and add a license to this Gist? Currently this is fully copyrighted by you (which is totally okay if that's intentional!). It's helpful if developers know exactly how this code is licensed.

Thanks!

Edit: Thanks for adding!

Hi @LeeKahSeng, I was wondering if there's any way to defined the access control of a keychain to allow access according to process signature ? I'd like to allow auto-login to keychain for specific processes and not necessarily users.

Thanks !

This would literally be one of the best written code fragments on the whole internet! I used the "coffee tip jar" found on the home page, https://swiftsenpai.com/development/persist-data-using-keychain/ THANKS, LEE SENG !!!!!!!!!