Thank you Dean for your help.
If I remove the ‘sso url’ setting, then going to the discourse page, Chrome gives me an error with “too many redirects”
I can remove the ‘sso secret’ safely (‘enable sso provider’ is not enabled).
I checked the app.yml settings.
The DISCOURSE_SAML_TARGET_URL is set with the same “sign-in URL” or “SSO URL” above.
The DISCOURSE_SAML_CERT_FINGERPRINT and DISCOURSE_SAML_CERT are set (correctly I hope, I went to SAML X.509 Certificate Fingerprint - Online SHA1 Decoder | SAMLTool.com to generate the fingerprint).
And DISCOURSE_SAML_FULL_SCREEN_LOGIN is set to true