We’re using Auth0 as a SSO SP for multiple customers to authenticate with our application. We have a SAML connection for one customer who is using Okta as an IdP. They are able to authenticate successfully via our application, but they get a 500 error from Auth0 when they try to perform IdP initiated SSO from Okta.
The strange thing is I can see a “Success Login” log entry in Auth0, but Auth0 throws a 500 and never redirects them to our application. You can see the generic Auth0 error page below. It’s cut off from the screenshot, but when the customer clicked the “view error details” link at the bottom of the page, there were no details.
We traced the requests being made. Here is a rough trace with some details removed:
-  GET https://.okta.com/… (IdP call to initiate SSO)
-  POST https://.auth0.com/login/callback?connection=
We compared the SAML payload from the POST request body to a SP-initiated SAML payload and they are identical. I can’t think of any other ways to debug this. Am I missing something?