After settings runAllManagedModulesForAllRequests for a ASP.NET web app all WebForms that have their URLs rewritten with Helicon URL rewrite no longer receive their parameters via postback calls.
It looks like these parameters are still available in Application_AuthenticateRequest Global.asax handler, but they are gone right after URL rewrite happens.
Any hints on how to solve this problem without undoing runAllManagedModulesForAllRequests setting?
Apparently Helicon module needs to be configured to handle URL rewrites in "Early Request Processing" mode to work with runAllManagedModulesForAllRequests setting.
This can be done by setting NotificationType=PREPROC_HEADERS flag at the beginning of Helicon's httpd.conf config file.
Read more: helicon docs, sitecoregadgets blogpost