Redirect to www and https in Pantheon server environments. Add to Drupal 7 settings.php file.

settings.php

/**
 * Pantheon HTTPS and www redirects.
 */
if (isset($_SERVER['PANTHEON_ENVIRONMENT']) && php_sapi_name() !== 'cli') {
  $domain = $_SERVER['HTTP_HOST'];
  $www_redirect = false;
  if (isset($_ENV['PANTHEON_ENVIRONMENT']) && $_ENV['PANTHEON_ENVIRONMENT'] === 'live') {
    if (count(explode('.', $domain)) < 3 && stripos($domain, 'www.') === false) {
      $domain = 'www.' . $domain;
      $www_redirect = true;
    }
  }

  if ($www_redirect || !isset($_SERVER['HTTP_X_SSL']) || $_SERVER['HTTP_X_SSL'] != 'ON' ) {
    header('HTTP/1.0 301 Moved Permanently');
    header('Location: https://'. $domain . $_SERVER['REQUEST_URI']);
    exit();
  }
}