Looks like the auth0-samples/auth0-regular-webapp-saml-idp-client repository was deleted. I still have it cloned locally and the git remote shows up as org-18199888@github.com:auth0-samples/auth0-regular-webapp-saml-idp-client.git
I have it forked here: GitHub - patkub/auth0-regular-webapp-saml-idp-client: Forked from auth0-samples
Is there a better sample app for testing Auth0 SAML clients?