OAuth2: How to do Authentication with Unsplash API

Question

I'm writing an iOS app to using Unsplash API. And I get below issue when dealing with authentication workflow(login via website):

Following Authorization workflow on Unsplash API, I could get authorization code on the redirect page.

1) What I opened: https://unsplash.com/oauth/authorize?client_id={myclientid}&redirect_uri=urn%3Aietf%3Awg%3Aoauth%3A2.0%3Aoob&response_type=code&scope=public

2) Safari get to the response page with Authorization code

3) Then I need to make a POST request to https://unsplash.com/oauth/token and include the Authorization code

/ / / My question is how to get the Authorization code in Step 2 with Swift?, I could deal with JSON response, but this is a page view in return, what class or method I should use to retrieve the code value?

/ / / Well, here is my code

class FancyClient {

    static let clientID = "clientID"
    static let clientSceret = "clientSceret"

    struct Auth {
        static var accessToken = ""
        static var authorizationCode = ""
    }

    enum Endpoints {
        static let base = "https://unsplash.com"
        static let apiKeyParam = "?client_id=\(FancyClient.clientID)"
        static let apiSecretParam = "?client_secret=\(FancyClient.clientSceret)"

        case getAuthorizationCode
        case login
        case getAccessToken

        var stringValue: String {
            switch self {
            case .getAuthorizationCode:
                return Endpoints.base + "/oauth/authorize" + Endpoints.apiKeyParam + "&redirect_uri=urn%3Aietf%3Awg%3Aoauth%3A2.0%3Aoob" + "&response_type=code" + "&scope=public"
            case .getAccessToken:
                return Endpoints.base + "/oauth/token" + Endpoints.apiKeyParam + "&\(Endpoints.apiSecretParam)" + "&redirect_uri=fancyimage:authenticate" + "&code=\(Auth.authorizationCode)" + "grant_type=Value authorization_code"
            case .login:
                return ""
            }
        }

        var url: URL {
            return URL(string: stringValue)!
        }
    }

    class func getAccessToken(url: URL, completion: @escaping (Bool, Error?) -> Void ) {
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")

        let task = URLSession.shared.dataTask(with: request) { (data, response, error) in
            guard let data = data else {
                DispatchQueue.main.async {
                    completion(false, error)
                }
                return
            }
            do {
                let decoder = JSONDecoder()
                let responseObject = try decoder.decode(TokenResponse.self, from: data)
                Auth.accessToken = responseObject.accessToken
                DispatchQueue.main.async {
                    completion(true, nil)
                }
            } catch {
                DispatchQueue.main.async {
                    completion(false, error)
                }
            }
        }
        task.resume()
    }
}

class LoginViewController: UIViewController {


    @IBOutlet weak var loginViaWeb: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func loginViaWebsiteTapped(_ sender: Any) {
        print(FancyClient.Endpoints.getAuthorizationCode.url)
        UIApplication.shared.open(FancyClient.Endpoints.getAuthorizationCode.url, options: [:], completionHandler: nil)


        // if let authorizationCode = responsePage.authorizationCode {
            FancyClient.getAccessToken(url: FancyClient.Endpoints.getAccessToken.url) { (success, error) in
                // continue...
            }
        }

    }

}