「ハッカソン当日より前の開発環境の構築やプロトタイプの作成など、事前準備を可とします」とのことなので、ツイキャスハッカソン用にOauth2のログインでAccessTokenを取得するとこをSwift3で書きました

TwicastLoginWebViewController.swift

//
//  TwicastLoginWebViewController.swift
//  TwicasHackathonTest
//
//  Created by HanedaKentarou on 2017/01/16.
//  Copyright © 2017年 com.adriablue. All rights reserved.
//

/* How to use.

 ＊ Twicast API
 http://apiv2-doc.twitcasting.tv/#introduction
 
 ---------------------
 vc.loginCompleteion = { (credential:TwicastCredential?, error:Error?) in
    if let credential = credential{
        print(credential)
    }
 }
 ---------------------
 
 */

import UIKit

extension URL {
    var params: [String : String] {
        var results: [String : String] = [:]
        guard let urlComponents = NSURLComponents(string: self.absoluteString), let items = urlComponents.queryItems else {
            return results
        }
        
        for item in items {
            results[item.name] = item.value
        }
        
        return results
    }
}

struct TwicastCredential {
    let tokenType:String
    let expireDate:NSDate
    let accessToken:String
}

class LoginWebViewController: UIViewController {

    var webView:UIWebView = UIWebView()
    
    // API Info
    let CLIENT_ID     = "XXXXX"
    let CLIENT_SECRET = "XXXXX"
    let CSRF_TOKEN    = "XXXXX"
    let REDIRECT_URL  = "XXXXX"
    var loginURL:URL?{
        get{
            return URL(string: "https://apiv2.twitcasting.tv/oauth2/authorize?client_id=\(CLIENT_ID)&response_type=code&state=\(CSRF_TOKEN)")
        }
    }
    
    var loginCompleteion = { (credential:TwicastCredential?, error:Error?) in
    }
    
    // MARK: Lifecycle
    
    override func viewDidLoad() {
        super.viewDidLoad()
        webView = UIWebView(frame: self.view.bounds)
        webView.delegate = self
        self.view.addSubview(webView)
        
        if let requestURL = loginURL{
            webView.loadRequest(URLRequest(url: requestURL))
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

extension LoginWebViewController:UIWebViewDelegate{
    
    // MARK: WebView Delegate
    
    func webView(_ webView: UIWebView, shouldStartLoadWith request: URLRequest, navigationType: UIWebViewNavigationType) -> Bool {
        if let url = request.url, url.absoluteString.contains(REDIRECT_URL){
            if let code = url.params["code"]{
              requestAccessToken(code: code)
            }
        }
        return true
    }
    
     func requestAccessToken(code:String){
        
        let urlString = "https://apiv2.twitcasting.tv/oauth2/access_token"
        let request = NSMutableURLRequest(url: URL(string: urlString)!)
        
        // set the method(HTTP-POST)
        request.httpMethod = "POST"
        // set the header(s)
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")
        
        // set the request-body(JSON)
        let params: [String: String] = [
            "grant_type": "authorization_code",
            "client_id": CLIENT_ID,
            "client_secret": CLIENT_SECRET,
            "redirect_uri":REDIRECT_URL,
            "code":code
        ]
        request.httpBody = try! JSONSerialization.data(withJSONObject: params, options: JSONSerialization.WritingOptions.prettyPrinted)
        
        let task = URLSession.shared.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) in
            do {
                guard let resp = try JSONSerialization.jsonObject(with: data!, options: []) as? [String: AnyObject] else {
                    self.finish(credential: nil, error: error)
                    return
                }
                if let type = resp["token_type"] as? String,
                    let accessToken = resp["access_token"] as? String,
                    let expireIn = resp["expires_in"] as? Int{
                    let expireDate = NSDate(timeIntervalSinceNow: TimeInterval(expireIn))
                    let credential = TwicastCredential(tokenType: type, expireDate: expireDate, accessToken: accessToken)
                    self.finish(credential: credential, error: nil)
                }
                
                
            } catch  {
                self.finish(credential: nil, error: error)
                return
            }
        })
        task.resume()
    }
    
    func finish(credential:TwicastCredential?, error:Error?){
        self.loginCompleteion(credential, error)
        self.dismiss(animated: true, completion: nil)
    }
}