Hello,
I would recommend reviewing the thread here: https://www.googlecloudcommunity.com/gc/Apigee/using-OIDC-instead-of-SAML-for-apigeex-integrated-developer/m-p/861613#M81798 which notes that OIDC support within the integrated portal is not yet supported. Our product team is exploring the potential for support, and once we know more we will be sure to update, thanks!