You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: authentication.go
    path of file: ./repos/olivia/modules/spotify
    
    the code of the file until where you have to start completion: package spotify

import (
	"fmt"
	"net/http"
	"os"
	"time"

	"github.com/olivia-ai/olivia/util"

	"github.com/olivia-ai/olivia/user"
	"github.com/zmb3/spotify"
	"golang.org/x/oauth2"
)

var (
	redirectURL = os.Getenv(
    
func CompleteAuth(w http.ResponseWriter, r *http.Request) {
	token, err := auth.Token(state, r)

	if err != nil {
		http.Error(w, "Couldn't get token", http.StatusForbidden)
		tokenChannel <- &oauth2.Token{}
		return
	}

	if st := r.FormValue("state"); st != state {
		http.NotFound(w, r)
		tokenChannel <- &oauth2.Token{}
		return
	}

	// Use the token to get an authenticated client
	w.Header().Set("Content-Type", "text/html")
	// Redirect the user
	fmt.Fprintf(w, `<meta http-equiv="refresh" content="0; url = %s" />`, redirectURL)

	tokenChannel <- token
}