Shibboleth 2.5.3 SP looping after successful POST

[Peter Schober]

* Klingenstein, Nate <nklingenstein at calstate.edu> [2016-10-21 21:46]:
> My first guess is that you're accidentally protecting the
> /Shibboleth.sso tree with actual Shibboleth access control rules, so
> as soon as you get back to the SP, assertion in hand, it's
> recognized as attempted access to a protected resource, and 302,
> and...

The SP does not protect its own endpoints, ever, AFAIR.
Also the above doesn't match the OP's description where after
reciecing the POST a redirect to the root of the site is generated
(and not an authn request, that only comes after that).
-peter