This article describes on how to update Identity Provider Signature Certificate.
Email security cloud
Cloud Secure Web Gateway
Identity Provider Signature Certificate has been probably expired.
1. Navigate to your Account Security in Broadcom SaaS Portal and click on Blue Arrow for your identity provider configured domain. You find it under https://accounts.security.com/
2. Once clicking on the blue arrow, a new page will be popped up on your right, navigate to Account Details.
3. Your domain will be showing above Identity Provider, click on it and the IDP wizard will pop-up.
4. IDP configuration will show up for your domain and you can edit it and upload the Signature Ceritficate.