NetworkManager.swift

import Alamofire
class NetworkManager {
    static let shared: NetworkManager = {
        return NetworkManager()
    }()
    typealias completionHandler = ((Result<Data, CustomError>) -> Void)
    var request: Alamofire.Request?
    let retryLimit = 3
    let authorize = "https://api.petfinder.com/v2/oauth2/token"
    func authorize(parameters: [String: Any]?, completion: @escaping completionHandler) {
        request?.cancel()
        request = AF.request(authorize, method: .post, parameters: parameters, encoding: JSONEncoding.default).responseJSON { response in
            if let data = response.data {
                completion(.success(data))
            } else {
                completion(.failure(.unavailableServer))
            }
        }
    }
}