got a 401 when I get access token for LinkedIn - php

Question

$oauth->getAccessToken() causes Invalid auth/bad request (got a 401, expected HTTP/1.1 20X or a redirect).
How do I look at the request headers to figure out what exactly is wrong?
$oauth = new OAuth(CONSUMER_KEY, CONSUMER_SECRET);
$oauth->disableSSLChecks();
$request_token_response = $oauth->getRequestToken('https://api.linkedin.com/uas/oauth/requestToken');
if($request_token_response === FALSE) {
throw new Exception("Failed fetching request token, response was: " . $oauth->getLastResponse());
} else {
$request_token = $request_token_response;
var_dump($request_token);
if (!isset($_GET['oauth_verifier'])) {
$this->redirect("https://api.linkedin.com/uas/oauth/authorize?oauth_token=" . $request_token['oauth_token']);
} else {
$oauth_verifier = $_GET['oauth_verifier'];
$oauth->setToken($request_token['oauth_token'], $request_token['oauth_token_secret']);
$access_token_url = 'https://api.linkedin.com/uas/oauth/accessToken';
$access_token_response = $oauth->getAccessToken($access_token_url, "", $oauth_verifier);
if($access_token_response === FALSE) {
throw new Exception("Failed fetching request token, response was: " . $oauth->getLastResponse());
} else {
$access_token = $access_token_response;
$params = array();
$headers = array();
$method = OAUTH_HTTP_METHOD_GET;
// Specify LinkedIn API endpoint to retrieve your own profile
$url = "http://api.linkedin.com/v1/people/~";
// By default, the LinkedIn API responses are in XML format. If you prefer JSON, simply specify the format in your call
// $url = "http://api.linkedin.com/v1/people/~?format=json";
// Make call to LinkedIn to retrieve your own profile
$oauth->fetch($url, $params, $method, $headers);
echo $oauth->getLastResponse();
}
}
}
}

Answer 1

oauth_verifier only verifies the request_token from which it was obtained. I needed to store the original request_token in session instead of getting a new request_token on callback.