func handleOAuth2Callback(opts *Options, config *oauth2.Config, s sessions.Session, w http.ResponseWriter, r *http.Request) {
next := extractPath(r.URL.Query().Get("state"))
code := r.URL.Query().Get("code")
t, err := config.Exchange(oauth2.NoContext, code)
if err != nil {
// Pass the error message, or allow dev to provide its own
// error handler.
http.Redirect(w, r, PathError, http.StatusFound)
return
}
// Store the credentials in the session.
val, _ := json.Marshal(t)
s.Set(keyToken, val)
http.Redirect(w, r, next, http.StatusFound)
}
