Shibboleth 2.5.3 SP looping after successful POST

[Klingenstein, Nate]

And never mind, I didn't read the redirect to the site root as part of the loop.  Disregard my hunch.  Peter's right and his links will be more helpful.

Cookie issues are most probable, which could be causing you to both lose the intended destination and your session once it doesn't know where to send you and defaults to the site root.

You'll find the most useful debugging information in native.log.  Sorry for the bad lead.