以下の curl のコマンドを Swift で実現したいです。しかしヘッダ部分の記述方法がわかりません。

curl -X GET \
     --header "X-Auth-Token: abcdef" \
     https://devapi.thecurrencycloud.com/v2/rates/detailed?buy_currency=EUR&sell_currency=USD&fixed_side=buy&amount=1000

こちらが私のコードです。しかしエラーとなってしまいました。解決方法をご教示頂きたいです。

func exchangerate(){
    let token = "abcdef"
    let request = NSMutableURLRequest(URL: NSURL(string: "https://devapi.thecurrencycloud.com/v2/rates/detailed")!)
    var buyCurrency = "EUR"
    var sellCurrency = "USD"
    var fixSide = "buy"
    var amount = "1000"
    var postString:NSString = "buy_currency=\(buyCurrency)&sell_currency=\(sellCurrency)&fixed_side=\(fixSide)&amount=\(amount)"

    request.HTTPMethod = "GET"
    request.setValue(token, forHTTPHeaderField: "X-Auth-Token")
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)

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

        if error != nil {
            println("error=\(error)")
            return
        }

        println("response = \(response)")

        let responseStringExchangeRate = NSString(data: data, encoding: NSUTF8StringEncoding)
        println("responseStringExchangeRate = \(responseStringExchangeRate)")
    }
    task.resume()

}

エラー:

error=Error Domain=NSURLErrorDomain 
      Code=-1005 
      "The operation couldn’t be completed. (NSURLErrorDomain error -1005.)" 
      UserInfo=0x7fea7b4d63f0
      {
         NSErrorFailingURLStringKey=https://devapi.thecurrencycloud.com/v2/rates/detailed,
        NSErrorFailingURLKey=https://devapi.thecurrencycloud.com/v2/rates/detailed,             _kCFStreamErrorDomainKey=4,
        _kCFStreamErrorCodeKey=-4, 
        NSUnderlyingError=0x7fea7d805ba0
        "The operation couldn’t be completed. (kCFErrorDomainCFNetwork error -1005.)"
      }