In Apache web server when you add X-Forwarded-SSL request header at Apache web server level, sometimes it adds the header name to the Vary response header. This breaks CDN caching for Akamai and other CDN providers.
Apache / AEM Dispatcher module
The solution is to put a "no vary" flag on the mod_rewrite rules in the conf file that is checking the X-Forwarded-SSL header.
Copy of Apache HTTP Server documentation for this setting:
‘novary|NV’ (no vary): If a HTTP header is used in the condition, this flag prevents this header from being added to the Vary header of the response.