Is a query string parm allowed on SSO endpoint redirect URL?

[Mike Flynn]

I have an iDP that has this endpoint in their metadata:
<md:SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://sso.ttnlearning.com/EasyConnect/SSO/Post.aspx?idp=ElanBCGIDP" />


After authN comes back to my SP, I see this:
POST https://sso.ttnlearning.com/RESTServiceProvider/SSO/Post.aspx HTTP/1.1
Host: sso.ttnlearning.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:51.0) Gecko/20100101 Firefox/51.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Referer: https://sso.ttnlearning.com/EasyConnect/SSO/Redirect.aspx?SAMLRequest=fZJRT4MwFIX%2FCuk7FBAdNIMENxOXTEcG%2BuCL6boiTUqLvUW3fy8DNfPBPd70%0A3HN6vtw50FZ2JO9to7b8vedgnUMrFZDxIUW9UURTEEAUbTkQy0iZP6xJ6Pmk%0AM9pqpiVycgBurNBqoRX0LTclNx%2BC8aftOkWNtR0QjKERO08e1Z56TLe4HMad%0Altw2HoDGJ9cQF5uyQs5y%2BIZQ9GR4tg7as1ZJTo0S6m30uKNwHCIVZxaX5QZv%0A%2BV6YYfAodAfkrJYper1KYhYkNU9oFCVJVNdxGNQsiW%2FodRyG8WyQAfR8pcBS%0AZVMU%2BsHM9UPXT6ogJlFIAv8FOcV311uh9kP6ZTC7SQTkvqoKd%2Br0zA2MfQYB%0AyuYnvGQMNmfAL9vSH8oo%2B4cp%2FDJ1oZvjs5ApsSOPg%2BtqWWgp2NHJpdSfC8Op%0A5SkKEM6mlb%2F3kH0B%0A&RelayState=cookie%3Afa661613&SigAlg=http%3A%2F%2Fwww.w3.org%2F2000%2F09%2Fxmldsig%23rsa-sha1&Signature=amwLRNPbde7HjW6VP1A%2By1ADJR9b%2FBDtM6gGsNmbBa9qexdCpgn5C35wZEiV7KxEHQusLZ6okvWWdx0klKgQL7Fdpef7nrNHnibUKkd7Ry0Ky4QAd%2B4jbgLJK6zBaOwp87zuNxxZE9YuArW30N98zz5Qk5SQP2E1mYO3KJ67LY2HM8k8wnRBXRWTfQUePxYlJ%2BFuwE2%2BRsitWRwf7cHIfse6fwo6Fk2cqPR%2Biji5rIhFUFO6QzFuI1qAakRxONWBX20Nbf6xSeg6kqq%2BmJ4G%2Bg5QWbDh%2FPanHRh4FG3VivuwQkhs67ul47wAmh8Rg1CZpFyE7e7n7sLguinRjTt%2FqA%3D%3D
So the question is, why does it drop that parm?  Is this not allowed for an endpoint?
Thanks!
Mike
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