StrictServerWebExchangeFirewall breaks spring-cloud-gateways RemoveRequestHeaderGatewayFilterFactory

[sandra-markerud]

Describe the bug
With the update to spring-boot-3.3.5, our spring-cloud-gateway application breaks within the built-in "RemoveRequestHeaderGatewayFilterFactory". The exchange to be mutated is now a "StrictFirewallServerWebExchange". Those headers cannot be deleted anymore. Hence, the application throws an UnsupportedOperationException at org.springframework.http.ReadOnlyHttpHeaders.remove

To Reproduce
Within a spring-cloud-gateway application define a route that has the "RemoveRequestHeaderGatewayFilterFactory" applied. Is has to be secured using spring-security (e.g. oauth).

Expected behavior
No exception anymore but the filter to work again

Sample
https://github.com/sandra-markerud/spring-cloud-gateway-upgrade
The main branch contains a working application. The "RemoveRequestHeaderTest" shows, that everything works prior the upgrade. Additionally, the tooling folder contains a docker dompose file for a keycloak and mockserver and http requests for a live demo.
The spring-boot_3.3.5 branch upgrades the application to spring-boot-3.3.5 and now the tests fails with the mentioned exception.

[sjohnr]

Thanks @sandra-markerud. I believe this is a duplicate of gh-15989. See this comment for the workaround in the meantime. Please let me know if I have misunderstood anything.

[sandra-markerud]

Thanks @sjohnr
The proposed workaround works like a charm as I had indeed the same issue mentioned in the linked issue :)