Enhancement Proposal: Authentication Filter

docs/proposals/authentication-filter.md

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+# Enhancement Proposal-4052: Authentiation Filter
+
+- Issue: https://github.com/nginx/nginx-gateway-fabric/issues/4052
+- Status: Provisional
+
+## Summary
+
+Design and implement a means for users of NGINX Gateway Fabric to enable authentication on requests to their backend applications.
+This new filter should eventually expose all forms of authentication available through NGINX, both Open Source and Plus.
+
+## Goals
+
+- Design a means of configuring authentication for NGF
+- Design Authentication CRD with Basic Auth and JWT Auth in mind
+- Determine initial resource specification
+- Evaluate filter early in request processing, occurring before URLRewrite, header modifiers and backend selection
+- Authentication failures return appropriate status by default (e.g., 401/403)
+- Ensure response codes are configurable
+
+## Non-Goals
+
+- Design for OIDC Auth
+- An Auth filter for TCP and UDP routes