Make Spotify callback configurable

bot.go

 	SpotifyClientID     string
 	SpotifyClientSecret string
 	SpotifyUser         string
+	SpotifyCallback     string
 	ListenAddr          string
 }
 
 func (app *App) CreateSpotifyClient() *spotify.SpotifyClient {
 	spotifyClient := spotify.NewClient(app.credentials.SpotifyClientID, app.credentials.SpotifyClientSecret)
-	spotifyClient.SetupUserAuthenticate()
+	spotifyClient.SetupUserAuthenticate(app.credentials.SpotifyCallback)
 	return spotifyClient
 }
 

spotify/spotify.go

 	return nil
 }
 
-func (s *SpotifyClient) SetupUserAuthenticate() error {
+func (s *SpotifyClient) SetupUserAuthenticate(redirectURL string) error {
 	s.config = &oauth2.Config{
 		ClientID:     s.clientID,
 		ClientSecret: s.clientSecret,
-		RedirectURL:  "http://localhost:8080/callback",
+		RedirectURL:  redirectURL,
 		Scopes:       []string{"playlist-modify-public"},
 		Endpoint:     spotifyAuth.Endpoint,
 	}