Fail to decode saml authn request v3.2.1

[Rod Widdowson]

> Appreciate any pointers to get this resolved 

It looks to me like you have the wrong protocol going to the wrong end point

> https://xyz/idp/profile/Shibboleth/SSO
Requires TargetID and Shire on a normally configured machine.

> ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST">
Usually ends up at https://xyz/idp/profile/SAML2/POST/SSO

/Rod