A class that makes it easy to store and retrieve string values from the Keychain

Keychain.swift

import Foundation

/* Example Usage:
Get
----------------------------
let token = Keychain[.token]

Set
----------------------------
Keychain[.token] = value
Keychain[.token] = nil
*/

enum KeychainKey: String {
    case token
}

class Keychain {
    class subscript(key: KeychainKey) -> String? {
        get {
            return Keychain.getString(valueForKey: key.rawValue)
        }
        set {
            if let newValue = newValue {
                Keychain.setString(value: newValue, forKey: key.rawValue)
            } else {
                Keychain.removeString(forKey: key.rawValue)
            }
        }
    }
    
    class func setString(value: String, forKey key: String) {
        let data = Data(value.utf8)
        let query = getSetStringQuery(key: key, data: data)
        SecItemDelete(query as CFDictionary)
        SecItemAdd(query as CFDictionary, nil)
    }
    
    class func removeString(forKey key: String) {
        let query = getSetStringQuery(key: key)
        SecItemDelete(query as CFDictionary)
    }
    
    class func getString(valueForKey key: String) -> String? {
        let query = getGetStringQuery(key: key)
        var dataTypeRef: AnyObject? = nil
        let status: OSStatus = SecItemCopyMatching(query as CFDictionary, &dataTypeRef)
        if status == noErr {
            guard let data = dataTypeRef as? Data else { return nil }
            return String(data: data, encoding: .utf8)
        } else {
            return nil
        }
    }
    
    private class func getSetStringQuery(key: String, data: Data? = nil) -> CFDictionary {
        return [kSecClass as String: kSecClassGenericPassword as String,
                kSecAttrAccount as String: key,
                kSecValueData as String: data ?? Data()] as CFDictionary
    }
    
    private class func getGetStringQuery(key: String) -> CFDictionary {
        return [kSecClass as String: kSecClassGenericPassword,
                kSecAttrAccount as String: key,
                kSecReturnData as String: kCFBooleanTrue!,
                kSecMatchLimit as String: kSecMatchLimitOne] as CFDictionary
    }
}