How do I log into a site using a POST request? (Swift, IOS)

I want to create an iOS app that logs into a website and parses data from multiple pages of that site while keeping the login session.This is what I have done so far. I am sending a GET request to retrieve the EVENTVALIDATON and VIEWSTATE parameters required for the POST request. (I looked at POST using "Firebug"). When I run the following code, it returns the same login page. But he has to give me this page .

    var parameter: Parameters = [:]
    var viewstate: String = ""
    var eventvalidation: String = 


    @IBAction func postRequest(_ sender: Any) {


    Alamofire.request("https://ecampus.psgtech.ac.in/studzone/AttWfLoginPage.aspx").responseString { response in
        print("\(response.result.isSuccess)")
        if let html = response.result.value {
            if let doc = Kanna.HTML(html: html, encoding: String.Encoding.utf8) {
                // Search for nodes by CSS selector

                for show in doc.css("input[id='__VIEWSTATE']") {
                    self.viewstate=show["value"]!
                    //print(show["value"] as Any)
                }

                for show in doc.css("input[id='__EVENTVALIDATION']") {
                    self.eventvalidation=show["value"]!
                    //print(show["value"] as Any)
                }
            }
        }
        //creating dictionary for parameters
        self.parameter = ["__EVENTTARGET":"",
                         "__EVENTARGUMENT":"",
                         "__LASTFOCUS":"",
                         "__VIEWSTATE":self.viewstate,
                         "__EVENTVALIDATION":self.eventvalidation,
                         "rdolst":"S",
                         "Txtstudid":"<myrollno>",
                         "TxtPasswd":"<mypassword>",
                         "btnlogin":"Login"
        ]
    }
    Alamofire.request ("https://ecampus.psgtech.ac.in/studzone/AttWfLoginPage.aspx",method: .post, parameters: self.parameter, headers: headers).responseString { response in
        print("\(response.result.isSuccess)")
        print(response)
    }

      

        
        
        
      

    

To be honest, I am very new to queries and data analysis (I have partially ironed out some of the parsing). I did some more research and read about headers and cookies. Therefore, after checking the headers, the initial GET request by the browser has a response header

Cache-Control :   private
Content-Encoding :   gzip
Content-Length :   4992
Content-Type :   text/html; charset=utf-8
Date :   Sun, 18 Jun 2017 14:25:50 GMT
Server :    Microsoft-IIS/8.0
Set-Cookie :   .ASPXAUTH=; expires=Mon, 11-Oct-1999 18:30:00 GMT; path=/; HttpOnly
Vary :   Accept-Encoding
X-AspNet-Version :   4.0.30319
X-Powered-By :   ASP.NET

      

        
        
        
      

    

and request header

Accept :    text/html,application/xhtml+xml,application/xml;q=0.9;q=0.8
Accept-Encoding :   gzip, deflate, br
Accept-Language :   en-US,en;q=0.5
Connection :   keep-alive
Cookie :   ASP.NET_SessionId=urzugt0zliwkmz3ab1fxx1ja
Host :   ecampus.psgtech.ac.in
Upgrade-Insecure-Requests :   1
User-Agent :   Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:54.0) Gecko/20100101 Firefox/54.0`

      

        
        
        
      

    

The problem is I don't understand how the original GET request could have a token with it. If the request is executed first, should the response contain the one containing the token? I don't know what I am doing wrong and how to do it. I don't know if anything is missing at all. I only came here after trying everything I could think of. Any help would be greatly appreciated. Thank.