public function login($callback_url=NULL) {
		if (!$this->f3->exists('GET.oauth_token')) {
			$tokens = $this->requestToken();
			$this->setAuthToken($tokens['oauth_token'], $tokens['oauth_token_secret']);
			if(is_null($callback_url))
				$callback_url = $this->f3->get('SCHEME').'://'.$this->f3->get('HOST').
					$this->f3->get('URI');
			$this->authorize($callback_url);
		} else {
			return $this->accessToken();
		}
	}