I am attempting to create a custom identity provider (based on https://github.com/ITfoxtec/ITfoxtec.Identity.Saml2/tree/master/test/TestIdPCore) but using HTTT-POST binding. The issue I am having is that when the service provider tries to validate the authn response they are getting errors ("actual digest value does not match expected"). I have also attempted to use a third party tool validating the xml response and was getting an error like "The XML has been altered after signing."
I am signing the assertion on the response using a certificate in the key store on the server where the service is running.