Golang. How to automatically authorize my app to access spotify APIs? - http

Question

I've registered on Spotify my app and I obtained my credentials.
I'm using Spotify web api through zmb3/spotify Go wrapper.
const redirectURI = "http://localhost:8080/auth_callback" //Already registered
const CLIENT_ID = "myId"
const CLIENT_SECRET = "mySecret"
const STATE = "myState"
I have a local server (written in Golang) listening for requests on some routes. When I define routes, I create the Spotify Authenticator with desired scopes and I obtain the url.
If I print the authorize url to stdout and I click it (or also with copy and paste) redirectURI is correctly called!
Here is the code...
var auth spotify.Authenticator
var token *oauth2.Token
var client spotify.Client
var authorize_url string
func main(){
fmt.Println("[MAIN] Starting Server")
auth = spotify.NewAuthenticator(redirectURI, spotify.ScopeUserReadPrivate, spotify.ScopeUserTopRead)
auth.SetAuthInfo(CLIENT_ID, CLIENT_SECRET)
authorize_url = auth.AuthURL(STATE)
var wg sync.WaitGroup
router.HandleFunc("/authorize_spotify", authHandler)
router.HandleFunc("/auth_callback", completeAuth)
http.Handle("/", router)
wg.Add(1)
go start(&wg, 0)
defer wg.Wait()
fmt.Println("[MAIN] Running Server... " + url)
}
//SPOTIFY API MANAGEMENT
func completeAuth(w http.ResponseWriter, r *http.Request) {
fmt.Println("Authentication Redirect Received")
token, err := auth.Token(STATE, r)
if err != nil {
http.Error(w, "Couldn't get token", http.StatusForbidden)
log.Fatal(err)
}
if st := r.FormValue("state"); st != STATE {
http.NotFound(w, r)
log.Fatalf("State mismatch: %s != %s\n", st, STATE)
}
// use the token to get an authenticated client
println(token)
client = auth.NewClient(token)
}
Now I want to make /authorize_spotify automatically call the obtained url.
I wrote these two lines.
func authHandler(w http.ResponseWriter, r *http.Request){
fmt.Println("[AUTH - HANDLER]")
http.Redirect(w, r, authorize_url, 302)
}
However, when I contact localhost:8080/authorize_spotify
authHandler is NEVER Called (no output on stdout, despite the fmt.Println(...)).
Misteriously, I'm redirected to the redirectURI at the same way, but it fails.
Seeing network http exchanges I noted that the authorize_url that I printed is a bit different from the authorize request misteriously sent (in the latter the user-top-read scope is missing), that confirms that the authHandler is not called.
How can I achieve my token calling authorize_url from code?
Thanks in advance!