Drupal's bootstrap overrides SimpleSamlPHP's exception handler

[manarth]

When drupal_bootstrap() is invoked, Drupal's exception handler (_drupal_exception_handler()) replaces SimpleSamlPHP's exception handler (SimpleSAML_exception_handler()).

• When an invalid SSO request is received, SimpleSamlPHP throws an Exception.
• This is caught by Drupal's Exception handler, which attempts to generate a Drupal error page.
• The error page invokes Drupal's theme layer.
• If aggregate-css or aggregate-js is turned on, Drupal attempts to build the CSS/JS caches.
• The cache-generation attempts to call file_get_contents() on the relevant CSS/JS files.
• The file_get_contents() calls fail, because the current working directory is the SimpleSamlPHP service, not the Drupal docroot.
• This triggers multiple watchdog() calls to record the error.

The effect is multiple watchdog entries with messages such as

Warning: file_get_contents(misc/jquery.once.js): failed to open stream: No such file or directory in drupal_build_js_cache() (line 5049 of /var/www/includes/common.inc).