Example Alamofire request for login with constants string

BackendService.swift

//
//  BackendService.swift
//
//  Created by Vasiliy Savchuk on 27.01.17.
//  Copyright © 2017 All rights reserved.
//

enum API {
    static var token: String?
    static var tokenType: String?
    static let headers: HTTPHeaders = [
        "Authorization": "\(API.tokenType ?? "") \(API.token ?? "")"
    ]
}
    static func loginUser(email: String, password: String, handler:@escaping (JSON?, NSError?) -> Void) {
        
        let urlUserParameters: [String: String] = [Constant.JSON.Email: email,
                                                   Constant.JSON.Password: password,
                                                   Constant.JSON.ClientId : Constant.API.ClientId,
                                                   Constant.JSON.ClientSecret : Constant.API.ClientSecret]

        Alamofire.request("http://your.com", method: .post, parameters: urlUserParameters, encoding: URLEncoding.default, headers: nil).validate().responseJSON { response in
            
            if 422 == response.response?.statusCode {
                let error = NSError.init(domain: "", code: 422, userInfo: [ NSLocalizedDescriptionKey :  NSLocalizedString("Please create account", comment: "") ])
                handler(nil, error)
            } else if let JSONRequest = response.result.value {                
                let json = JSON(JSONRequest)
                let token = json["access_token"].stringValue
                let tokenType = json["token_type"].stringValue
                API.token = token
                API.tokenType = tokenType
                
                handler(json, nil)
            } else {
                handler(nil, response.result.error as NSError?)
            }
        }
    }