We have Exchange 2013 CU17 setup on Windows Server 2012 R2 with CAS and mailbox being on two different machines. We have developed a HTTP module for performing some tasks. Both native ECP and OWA works fine without the custom HTTP module. But when custom module is enabled, OWA works fine but ECP throws the following exception :
Custom module invokes /ecp/auth/owaauth.dll which further invokes ecp/
The same is followed for OWA. It invokes /owa/auth/owaauth.dll which further invokes owa/ and it works fine.
Basic authentication is being used.
Any information on NeedCrossSiteRedirect function of owaauth.dll should do.