Login to Based Security and click Certificate Authorities, or browse to https://<CUSTOMER>.basedsec.io/cas
Copy the value of the SSH Certificate Authority
Login to your GitHub Enterprise or Organization, and navigate to Settings, then Authentication Security
https://github.com/enterprises/<CUSTOMER>/settings/security
OR
https://github.com/organizations/<CUSTOMER>/settings/security
Find the SSH certificate authorities section and click New certificate authority
Paste the value retrieved from the Based UI and click Save
Enable Require SSH Certificates and click save (Optional)