Migrating to new Web server; nothing happens after initiation of SSO to partner IDP

SAML Trace shows the response in firefox, but it just dumps be back to my main sign in page.
Everything should be a like for like from the old server to the new, but I’m clearly missing something.

Just not seeing an error to go off of??

Action: ReceiveSamlResponse
Partner name: https://idp.classlink.com/sso/metadata/YjFq#####
Relay state:
In response to: _01160ee6-bca3-43c4-8d77-c639837a26e3

ComponentSpace.SAML2 Verbose: 0 : 9316/62: 8/19/2023 6:21:32 PM: Initiation of SSO to the partner identity provider https://idp.classlink.com/sso/metadata/YjFqa##### has completed successfully.

If I’m understanding correctly, you’re seeing the HTTP Post of the SAML response in the browser SAML trace but it’s not being received at your application’s endpoint. The SAML library log shows the SAML authn request being sent but not the SAML response being received. Presumably this means the HTTP Post isn’t being received at your assertion consumer service endpoint.

I suggest using the browser developer tools to capture the network traffic to see exactly what happens after the HTTP Post of the SAML response. The browser must end up somewhere.

If it does end up at your assertion consumer service endpoint, I suggest adding some logging to your application to see whether it’s calling SAMLServiceProvider.ReceiveSSO. If it is, there should be entries in the SAML log file showing this.