Spotify token swap : unsupported URL error - ios

Question

I'm trying to implement the token swap and refresh for the Spotify sdk. I'm using the Heroku app as a server. Here is my code.
In my Sign-in view controller:
var auth = SPTAuth.defaultInstance()!
var session: SPTSession!
var player: SPTAudioStreamingController?
SPTAuth.defaultInstance().clientID = "********************************"
SPTAuth.defaultInstance().redirectURL = URL(string: "viraj-project2://callback" )
SPTAuth.defaultInstance().tokenSwapURL = URL(string: "https://viraj-project2.herokuapp.com/v1/swap")
SPTAuth.defaultInstance().tokenRefreshURL = URL(string: "https://viraj-project2.herokuapp.com/v1/refresh")
SPTAuth.defaultInstance().requestedScopes = [SPTAuthStreamingScope, SPTAuthPlaylistReadPrivateScope, SPTAuthPlaylistModifyPublicScope, SPTAuthPlaylistModifyPrivateScope, SPTAuthUserLibraryReadScope, SPTAuthUserLibraryModifyScope]
loginUrl = SPTAuth.defaultInstance().spotifyWebAuthenticationURL()
#IBAction func signIn(_ sender: Any) {
self.performSegue(withIdentifier: "toNewsFeed", sender: self)
if SPTAuth.supportsApplicationAuthentication() {
UIApplication.shared.open(loginUrl!, options: [:], completionHandler: nil)
} else {
if UIApplication.shared.openURL(loginUrl!) {
if auth.canHandle(auth.redirectURL) {
// To do - build in error handling
}
}
}
}
and in my AppDelegate
class AppDelegate: UIResponder, UIApplicationDelegate{
var window: UIWindow?
var auth = SPTAuth()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
auth.redirectURL = URL(string: "viraj-project2")
auth.sessionUserDefaultsKey = "current session"
// Override point for customization after application launch.
return true
}
func application(_ application: UIApplication, open url: URL, options: [UIApplicationOpenURLOptionsKey : Any] = [:]) -> Bool {
// 2- check if app can handle redirect URL
if auth.canHandle(auth.redirectURL) {
// 3 - handle callback in closure
print (url)
auth.handleAuthCallback(withTriggeredAuthURL: url, callback: { (error, session) in
// 4- handle error
if error != nil {
print(error)
print("error!")
}
NotificationCenter.default.post(name: Notification.Name(rawValue: "loggedinperformsegue"), object: nil)
// 5- Add session to User Defaults
let userDefaults = UserDefaults.standard
let sessionData = NSKeyedArchiver.archivedData(withRootObject: session!)
userDefaults.set(sessionData, forKey: "SpotifySession")
userDefaults.synchronize()
// 6 - Tell notification center login is successful
NotificationCenter.default.post(name: Notification.Name(rawValue: "loginSuccessfull"), object: nil)
})
return true
}
return false
}
The authentication works fine without adding the swap and refresh URLs. But whenever I run it with the two URLS added to the SPTAuth.defaultInstance() I get a unsupported URL error like so:
viraj-project2://callback/?code=AQDhKLE9s5GQGITEn**********5_y9aKZM6_nSlzA
2018-09-14 16:55:08.258063-0400 Project2[17606:3197471] NSURLConnection finished with error - code -1002
Optional(Error Domain=NSURLErrorDomain Code=-1002 "unsupported URL" UserInfo={NSLocalizedDescription=unsupported URL, NSUnderlyingError=0x109385130 {Error Domain=kCFErrorDomainCFNetwork Code=-1002 "unsupported URL" UserInfo={NSLocalizedDescription=unsupported URL}}})
error!
Can someone help?
Update on further digging:
When I include add the tokenSwapURL and tokenRefreshURL to my default instance the loginUrl formed looks like so
"https://accounts.spotify.com/authorize?nolinks=true&nosignup=true&response_type=code&scope=streaming%20playlist-read-private%20playlist-modify-public%20playlist-modify-private%20user-library-read%20user-library-modify&utm_source=spotify-sdk&utm_medium=ios-sdk&utm_campaign=ios-sdk&redirect_uri=viraj-project2%3A%2F%2Fcallback&show_dialog=true&client_id=****************"
The response type is "code" which as per the documentation is the right one according to Authorization Flow. But this is what returns the unsupported URL error.
Without the swap and refresh URLs the loginURL looks the same except that the response_type says "token". And this works fine. Is that right though? Doesn't response_type = token mean implicit grant flow?
https://developer.spotify.com/documentation/general/guides/authorization-guide/#client-credentials-flow