A SimpleSAMLphp Asset helper to produce MD5-fingerprinted URLs to assets. This allows long-term agressive caching by the browser while retaining instantaneous refreshing when the asset changes. Put this file in some SSP module's lib directory and rename the class name to match the module name (e.g. sspmod_mymodule_Asset).

Asset.php

<?php

/**
 * Helper class for working with Assets
 *
 * @author Laas Toom, University of tartu
 */
class sspmod_utmodule_Asset {
  /**
   * Get absolute URL to a specified asset.
   *
   * This function creates an absolute URL to a resource stored under ".../modules/<module>/www/".
   * Additionally, when {@param $parameters}['fingerprint'] is set, the asset will be fingerprinted with MD5. e.g.:
   *
   *   module/style.css -> module/style-c743acf9494efdcd97a17229f3fcd8f1.css
   *
   * Use following Apache RewriteRule to ditch this fingerprint on server:
   *   RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} !-d
   *   RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} !-f
   *   RewriteRule ^(.+)-[0-9a-f]{32}\.(css|js)$ $1.$2 [PT]
   *
   * @param string $resource  Resource path, on the form "<module name>/<resource>"
   * @param array $parameters  Extra parameters which should be added to the URL. Optional.
   * @return string  The absolute URL to the given resource.
   */
  public static function getAssetUrl($resource, array $parameters = array()) {
    assert('is_string($resource)');
    assert('$resource[0] !== "/"');
    $fingerprint = false;

    if (array_key_exists('fingerprint', $parameters)){
      $fingerprint = array_key_exists('fingerprint', $parameters);
      # Remove it from parameters
      unset($parameters['fingerprint']);
    }

    // apply fingerprint to resource name
    if ($fingerprint) {
      list($module_name, $asset_name) = explode("/", $resource);
      $module_basedir = SimpleSAML_Module::getModuleDir($module_name);
      $asset_file = $module_basedir . "/www/" . $asset_name;
      // only try to hash existing files
      if (file_exists($asset_file)) {
        $asset_md5 = file_exists($asset_file) ? "-" . md5_file($asset_file) : "";
        $resource = preg_replace("/\.([^.]+)$/", "$asset_md5.$1", $resource); 
      }
    }

    $url = SimpleSAML_Module::getModuleUrl($resource, $parameters);
    return $url;
  }
}