How can I add user's location to the request URL instead of hardcoding latitude and longitude?

import UIKit
import CoreLocation

var lat = ""
var long = ""

extension CurrentWeather {
    var temperatureString: String {
        return "\(Int(temperature))º"
    }

    var humidityString: String {
        let percentageValue = Int(humidity * 100)
        return "\(percentageValue)%"
    }

    var precipitationProbabilityString: String {
        let percentageValue = Int(precipitationProbability * 100)
        return "\(percentageValue)%"
    }
}

class ViewController: UIViewController, CLLocationManagerDelegate {

    @IBOutlet weak var currentTemperatureLabel: UILabel!
    @IBOutlet weak var currentHumidityLabel: UILabel!
    @IBOutlet weak var currentPrecipitationLabel: UILabel!
    @IBOutlet weak var currentWeatherIcon: UIImageView!
    @IBOutlet weak var currentSummaryLabel: UILabel!
    @IBOutlet weak var refreshButton: UIButton!
    @IBOutlet weak var activityIndicator: UIActivityIndicatorView!

    @IBOutlet weak var city: UILabel!
    @IBOutlet weak var state: UILabel!



    private let forecastAPI = "8a2bc5e53cc044aeefcfbabb13733561"

    // loaction manager and lat and longitude vars
    let locationManager = CLLocationManager()




    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let icon = WeatherIcon.PartlyCloudyDay.image
        let currentWeather = CurrentWeather(temperature: 56.0, humidity: 1.0, precipitationProbability: 1.0, summary: "Wet and rainy!", icon: icon)

        display(currentWeather)

        // instantiate loaction manager
        locationManager.delegate = self;
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.requestAlwaysAuthorization()
        locationManager.startUpdatingLocation()

        // creating baseURL and forecastURL
        let baseURL = NSURL(string: "https://api.darksky.net/forecast/\(forecastAPI)/")

        let forecastURL = NSURL(string: "\(lat),\(long)", relativeToURL: baseURL)

        print(forecastURL?.description)

    }


    func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        let location: CLLocationCoordinate2D = locationManager.location!.coordinate
        print("locations = \(location.latitude) \(location.longitude)")

        lat = String(location.latitude)
        long = String(location.longitude)


        // get the street number, geocode
        let geoCoder = CLGeocoder()
        let locationAddress = CLLocation(latitude: location.latitude, longitude: location.longitude)

        geoCoder.reverseGeocodeLocation(locationAddress) { (placemarks, error) in
            // Place details
            var placeMark: CLPlacemark!
            placeMark = placemarks?[0]

            // Address dictionary
            //print(placeMark.addressDictionary)

            // City
            if let city = placeMark.addressDictionary!["City"] as? NSString {
                self.city.text! = city as String
            }

            // Zip code
            if let zip = placeMark.addressDictionary!["State"] as? NSString {
                self.state.text! = zip as String

            }

        }


    }