func login(f *oauth2.Options, s sessions.Session, w http.ResponseWriter, r *http.Request) {
next := extractPath(r.URL.Query().Get(keyNextPage))
if s.Get(keyToken) == nil {
// User is not logged in.
if next == "" {
next = "/"
}
http.Redirect(w, r, f.AuthCodeURL(next, "", ""), codeRedirect)
return
}
// No need to login, redirect to the next page.
http.Redirect(w, r, next, codeRedirect)
}
