Combine with SSL for SaaS
If your application is using a custom hostname — meaning your SaaS provider is using SSL for SaaS — your application can support a waiting room.
Applications on Cloudflare
If your application is already using Cloudflare, create a waiting room using the normal process
Applications not on Cloudflare
If your application is not using Cloudflare, you need to ask your SaaS provider to configure a waiting room on their SSL for SaaS zone (using your custom hostname as the Hostname value).