Craig Brookes In APNs (and for Apns Feedback), the HTTP Proxy type is supported:
https://github.com/notnoop/java-apns/blob/180a190d4cb49458441596ca7c69d50ec7f1dba5/src/main/java/com/notnoop/apns/internal/ApnsConnectionImpl.java#L272-L275

Including proxy username/password.

I am not sure, however, if a global override "automatically" works, tbh

If not, a fairly minimal change is needed, explicitly reading the Environment Variable / System property is needed.