Generates a user agent string with a HMAC and timestamp for simpletest.
function drupal_generate_test_ua($prefix) {
static $key;
if (!isset($key)) {
// Use the salt from settings.php to create the HMAC key, since no services
// are available yet. The file properties add more entropy not easily
// accessible to others.
$key = drupal_get_hash_salt() . filectime(__FILE__) . fileinode(__FILE__);
}
// Generate a moderately secure HMAC based on the database credentials.
$salt = uniqid('', TRUE);
$check_string = $prefix . ';' . time() . ';' . $salt;
return $check_string . ';' . drupal_hmac_base64($check_string, $key);
}