Hostname mismatch against the apex hostname herokuapp.com

Issue

I can no longer access my app through https matching the apex hostname herokuapp.com with the SSL certificate through a CDN.

Resolution

Heroku recommends adding the custom domain (e.g., custom.example.com) to your app and use

• the DNS target as specified by the platform (e.g., haiku-sushi-123.herokudns.com) as the origin host,
• the custom domain for SNI,
• match the custom domain with the SSL certificate on Heroku, and
• use the custom domain for the Host request header.

Alternatively, it is possible to use the default domain (<appname>.herokuapp.com). However, the apex hostname herokuapp.com (without the subdomain) has been removed from the wild card certificate for *.herokuapp.com Heroku updated on June 1st, 2021.