IOS after post request get error with additional symbol "\"

I want to make a post request to my server. But when I get the response the server says that I sent wrong data. My code where I make the request is:

let urlAddress = Constants.API_DOMEN + Constants.SOC_LOGIN_ENDING
let request = NSMutableURLRequest(URL : NSURL(string: urlAddress)!)
let session = NSURLSession.sharedSession()

request.HTTPMethod = "POST"        

let params = [Constants.NAME : name,
              Constants.EMAIL: email,
              Constants.PROVIDER: provider,
              Constants.UID: userId,
              Constants.PHONE_NUMBER: phoneNumber,
              Constants.AVATAR: photoURL,
              Constants.TYPE: "3",
              Constants.KEY: getMD5Hash(userId, provider: provider)]
            as Dictionary<String, String>

request.HTTPBody = try! NSJSONSerialization.dataWithJSONObject(params, options: [])
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")


let task = session.dataTaskWithRequest(request){ data, response, error in
....

But when i get the response

...
let task = session.dataTaskWithRequest(request){ data, response, error in
            guard data != nil else {
                print("no data found: \(error)")
                return
            }
            
            let dataString = NSString(data: data!, encoding: NSUTF8StringEncoding)
.....

I see :

 dataString NSString?   "{\"head\": {\"errcode\": 400}, \"postdata\": 
    {\"oe\": [\"57AE2750\\\",\\\"phone\\\":\\\"\\\",
    \\\"name\\\":\\\"\\u0418\\u043b\\u044c\\u044f \\u041c\\u044f\\u0441\\u043e\\u0435\\u0434\\u043e\\u0432\\\",
    \\\"provider\\\":\\\"facebook\\\",
    \\\"uid\\\":\\\"236653050055667\\\",
    \\\"type\\\":\\\"3\\\",
    \\\"key\\\":\\\"b182111b0cf5d2b0e652675eac544490\\\"}\"], \"{\\\"email\\\":\\\"\\\",\\\"avatar\\\":
\\\"https:\\\\/\\\\/scontent.xx.fbcdn.net\\\\/hprofile-xfa1\\\\/v\\\\/t1.0-1\\\\/s200x200\\\\/10354686_10150004552801856_220367501106153455_n.jpg?oh\": [\"e809266ec7a9e37c304ff6ec183b735b\"]},
 \"error\": {\"name\": 401, \"type\": 401,
 \"uid\": 401, \"key\": 401, \"provider\": 401}}"

1. In field name I get wrong symbols.I suppose that something wrong with encoding here.

2. IOS is adding symbol "" to every quote. But I can't understand why.

Grateful for any help!

I found the solution. The right way to make a post request is shown below. I have added the complete function:

class func socialSignIn(name : String!, email: String!, provider: String!, userId: String!, photoURL: String!, phoneNumber: String!){
        var globalSuccess:Bool = false
        let urlAddress = Constants.API_DOMEN + Constants.SOC_LOGIN_ENDING
        let request = NSMutableURLRequest(URL : NSURL(string: urlAddress)!)
        let session = NSURLSession.sharedSession()

        request.HTTPMethod = "POST"

        var postString = Constants.NAME + "=" + name + "&";
        postString = postString + Constants.EMAIL + "=" + email + "&";
        postString = postString + Constants.PROVIDER + "=" + provider + "&";
        postString = postString + Constants.UID + "=" + userId + "&";
        postString = postString + Constants.PHONE_NUMBER + "=" + phoneNumber + "&";
        postString = postString + Constants.AVATAR + "=" + photoURL + "&";
        postString = postString + Constants.TYPE + "=" + "3" + "&";
        postString = postString + Constants.KEY + "=" + getMD5Hash(userId, provider: provider);


        request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")
        request.addValue("application/json", forHTTPHeaderField: "Accept")

        let task = session.dataTaskWithRequest(request){ data, response, error in
            guard data != nil else {
                print("no data found: \(error)")
                return
            }            

            //get user cookies
            let sessionId = getSessionId(response!)
            PreferencesHelper.setAuthToken(sessionId)

            do {
                if let json = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? NSDictionary{
                    let success = json.objectForKey("head")?.objectForKey("errcode") as? Int
                    if success == Constants.SUCCESS {
                        globalSuccess = true
                    }
                    print("Success: \(success)")
                }else{
                    let jsonStr = NSString(data: data!, encoding: NSUTF8StringEncoding)    // No error thrown, but not NSDictionary
                    print("Error could not parse JSON: \(jsonStr)")
                }
            } catch let parseError{
                print(parseError)                                                          // Log the error thrown by `JSONObjectWithData`
                let jsonStr = NSString(data: data!, encoding: NSUTF8StringEncoding)
                print("Error could not parse JSON: '\(jsonStr)'")
            }

            NSNotificationCenter.defaultCenter().postNotificationName(ViewController.notificationResult, object: nil, userInfo:[Constants.SUCCESS:globalSuccess ])
        }


        task.resume()
}

The function that gets the session id looks like:

class func getSessionId(response: NSObject)->String{
        if let httpResponse = response as? NSHTTPURLResponse{
            if let headers = httpResponse.allHeaderFields as? [String:String], url = httpResponse.URL{
                let cookies = NSHTTPCookie.cookiesWithResponseHeaderFields(headers, forURL: url)
                for cookie in cookies{
                    var cookieProperties = [String: AnyObject]()
                    cookieProperties[NSHTTPCookieName] = cookie.name
                    if (cookie.name == "sessionid"){
                        return cookie.value
                    }
                }
            }
        }

        return ""
    }