v2 Invalid Header support
As V2 is built on NGINx, it's resulted in at least one undocumented breaking change.
AGW v2 has the NGINX flag ignoreinvalidheaders flag enabled. This results in headers containing a period being dropped.
Whilst this might not be best practice, they're not technically invalid and this is something we have for historic reasons and makes it impossible to move to v2 without changing a lot of code.
Making this setting configurable or disabling by default for backward compatibility with v1 would be welcome as I'm sure v1 App Gateways will be retired at some point.