TwitterOAuth::getRequestToken PHP Method

    function getRequestToken($oauth_callback)
    {
        $parameters = array();
        $parameters['oauth_callback'] = $oauth_callback;
        $request = $this->oAuthRequest($this->requestTokenURL(), 'GET', $parameters);
        $token = OAuthUtil::parse_parameters($request);
        $this->token = new OAuthConsumer($token['oauth_token'], $token['oauth_token_secret']);
        return $token;
    }

/**
 * Method for Twitter login
 */
function ie_api_twitter_login()
{
    // Test user is logged in
    if (!iewp_api_user_is_logged_in()) {
        die('Error: please sign in');
    }
    // Twitter app credentials
    $consumer_key = trim(get_option('iewp_api_twitterapp_consumer_key', ''));
    $consumer_secret = trim(get_option('iewp_api_twitterapp_consumer_secret', ''));
    $callback_url = site_url('wp-json/ie-api/twitter-callback');
    // Test app creds have been set
    if ($consumer_key == '' || $consumer_secret == '') {
        die('Error: invalid twitter app credentials');
    }
    // Get a request token
    $connection = new TwitterOAuth($consumer_key, $consumer_secret);
    $request_token = $connection->getRequestToken($callback_url);
    // Store the request token for use in callback
    $user_id = iewp_api_id_from_hash();
    update_user_meta($user_id, 'twitter_oauth_token', $request_token['oauth_token']);
    update_user_meta($user_id, 'twitter_oauth_token_secret', $request_token['oauth_token_secret']);
    // Redirect to Twitter app approval page
    $redirect_url = $connection->getAuthorizeURL($request_token);
    wp_redirect($redirect_url);
    exit;
}