There's a statement in the below article that Exchange 2013 "out of the box" works just fine behind TMG when TMG is configured for delegated auth using NTLM. It explains that FBA and Windows Integrated auth are both enabled for OWA/ECP.
Can anybody confirm that this is still the case? I'm experiencing double prompt with TMG and Exchange 2013 (CU8) forms. I notice that Windows Integrated is disabled, and if I enable it FBA is automatically disabled (just like in 2010).