AssertionConsumerService giving "Not HTTP POST Method"

I've implemented the MitId login with your nuget package. It seems to work fine until we get redirected back to the AssertionConsumerService endpoint. There I get "Not HTTP POST Method" but with your code repo I do not... there everything works fine..

Now I'm wondering whether it might be an issue with the metadata Service Provider XML file, or the wrong issuer in appsettings.js or something else that is configurable... because the code is pretty much identical to your code examples....

Do you have any idea what the problem might be? Does the Issuer need to be registered in the MitId administration portal somewhere? I do not know how the Issuer is supposed to be configured.

I followed your step by step guide on how to implement and used you code example repos to test with and also to copy and tweak the code from...

NemLog-in should use POST binding when calling back to the AssertionConsumerService endpoint.

It is configured in the SP metadata (your applications metadata):
https://github.com/ITfoxtec/ITfoxtec.Identity.Saml2/blob/master/test/TestWebAppCoreNemLogin3Sp/Controllers/MetadataController.cs#L48

The SP metadata is uploaded to NemLog-in. The SP metadata include issuer, certificate(s) and endpoints.

And the AssertionConsumerService endpoint in you application is set to accept POST messages:
https://github.com/ITfoxtec/ITfoxtec.Identity.Saml2/blob/master/test/TestWebAppCoreNemLogin3Sp/Controllers/AuthController.cs#L57