Have a look at the Exchange 2010-2013 deployment guide. It has the manual steps to set this up. (Albeit from a standalone POV using APM+LTM, not a full-access webtop, but the SSO stuff should still work)
The deployment guide is at HERE It's not the easiest thing to follow with quite a few twists, turns and otherwise. And ignores anything like securid auth while trying to convince you to use the iApp, but it does have the manual config requirements in there for OWA SSO... It's just difficult to parse through to find the right ones (OR at least I found that, possibly because it makes assumptions about more Exchange knowledge than I'd care to admit to).
H