Token Storage in Swift

Token.swift

//
//  Token.swift
//
//  Created by Lee Irvine on 8/29/18.
//  Copyright © 2018 kezzi.co. All rights reserved.
//

import Foundation
import Security

struct TokenError: Error {
    let message: String
}

class Token: NSObject {

    private class func tokenId() -> String! {
        guard let appId = Bundle.main.bundleIdentifier else {
            print("Token: App ID missing from Bundle")
            return nil
        }

        return "\(appId).token"
    }

    class func set(_ value: String, server: String) {

        var query = [String: Any]()
        query[kSecClass as String] = kSecClassInternetPassword
        query[kSecAttrAccount as String] = self.tokenId()
        query[kSecAttrServer as String] = server
        query[kSecValueData as String] = value.data(using: .utf8)

        // Must delete. Not possible to explicitly overwrite.
        SecItemDelete(query as CFDictionary)

        let status = SecItemAdd(query as CFDictionary, nil)
        if status != errSecSuccess {
            print("failed to store key \(status)")
        }

    }

    class func get(server: String) -> String? {
        var query = [String: Any]()
        query[kSecClass as String] = kSecClassInternetPassword
        query[kSecAttrAccount as String] = self.tokenId()
        query[kSecAttrServer as String] = server

        query[kSecReturnData as String] = true
        query[kSecReturnAttributes as String] = true

        var item: CFTypeRef?
        let status = SecItemCopyMatching(query as CFDictionary, &item)

        if status == errSecItemNotFound {
            return nil
        }

        guard status == errSecSuccess else {
            print("Token: failed to load key \(status)")
            return nil
        }

        guard let existingItem = item as? [String : Any] else {
            print("Token: no token found in keychain")
            return nil
        }

        guard let tokenData = existingItem[kSecValueData as String] as? Data else {
            print("Token: token data missing")
            return nil
        }

        guard let token = String(data: tokenData, encoding: .utf8) else {
            print("Token: failed to decode token")
            return nil
        }

        return token
    }

    class func destroy(server: String) {
        var query = [String: Any]()
        query[kSecClass as String] = kSecClassInternetPassword
        query[kSecAttrAccount as String] = self.tokenId()
        query[kSecAttrServer as String] = server

        SecItemDelete(query as CFDictionary)
    }

}