This problem may be related to the UrlRoutingModule handling all the routing and bypassing SiteMinder. Any ideas on how may I be able to make SiteMinder's webagent handle the HTTP request before MVC's default request handler?
<system.webServer>
<!-- SM Server Config -->
<validation validateIntegratedModeConfiguration="false" />
<handlers>
<add name="wa-handler" path="*" verb="*" type="" modules="IsapiModule" scriptProcessor="%NETE_WA_PATH%\ISAPI6WebAgent.dll"
resourceType="Unspecified" requireAccess="None" allowPathInfo="false" preCondition="" responseBufferLimit="4194304" />
</handlers>
<modules>
<remove name="FormsAuthentication" />
</modules>
</system.webServer>
Issue Resolved: Apparently, for SiteMinder to protect ASP.NET MVC Apps, it must be upgraded to version R12.5 / WebAgent 7 or higher. Just update SiteMinder on your IIS server and it should start working.