Support headers with underscore

[arkodg]

Description:

Describe the desired behavior, what scenario it enables and how it
would be used.

Rejected by default in Envoy Gateway to align with best practices https://www.envoyproxy.io/docs/envoy/latest/configuration/best_practices/edge

An opt in field to enable/allow this would be great
https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/protocol.proto#enum-config-core-v3-httpprotocoloptions-headerswithunderscoresaction

[optional Relevant Links:]

Any extra documentation required to understand the issue.

[arkodg]

https://gateway.envoyproxy.io/v1.0.0/api/extension_types/#headersettings can be a good home for this field

[guydc]

+1 for general transparency reasons. Is there a concrete use case that you're aware of?

[arkodg]

• yeah this was requested by a user, dont have any details on the exact header name
• also trying to get parity with ingress NGINX
  https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#enable-underscores-in-headers

[ardikabs]

can i work on this, @arkodg ? for context, I have encountered a use case in a legacy system with ingress Nginx that relying to underscore headers, and to address it, I made modifications to the xDS using an Envoy gateway extension service.

[arkodg]

looks like David beat you to it :)
#3052

[davidalger]

Oh nice, hadn't seen this opened when I implemented the knob. Glad I could help someone else out with the addition!

We had path_normalization_failed show up in response_code_details for requests coming from a handful of customer API integrations after putting EG into production and had temporarily solved it with an XDS patch.