Add initial scaffolding

Signed-off-by: José Ulises Niño Rivera <junr03@users.noreply.github.com>

envoyfilter/README.md

@@ -1 +1,60 @@
-Envoy filter code for gateway
+# Envoy filter code for gateway
+
+## Building
+
+```sh
+$ cargo build --target wasm32-wasi --release
+```
+
+## Using in Envoy
+
+This example can be run with [`docker compose`](https://docs.docker.com/compose/install/)
+and has a matching Envoy configuration.
+
+```sh
+$ docker compose up
+```
+
+## Examples
+
+### Direct response.
+
+Send HTTP request to `localhost:10000/hello`:
+
+```sh
+$ curl localhost:10000/hello
+```
+
+Expected response:
+
+```console
+HTTP/1.1 200 OK
+content-length: 40
+content-type: text/plain
+custom-header: katanemo filter
+date: Wed, 10 Jul 2024 16:59:43 GMT
+server: envoy
+```
+
+### Inline call.
+
+Send HTTP request to `localhost:10000/inline`:
+
+```sh
+$ curl localhost:10000/hello
+{
+  "headers": {
+    "Accept": "*/*",
+    "Host": "localhost",
+    "User-Agent": "curl/7.81.0",
+    "X-Amzn-Trace-Id": "Root=1-637c4767-6e31776a0b407a0219b5b570",
+    "X-Envoy-Expected-Rq-Timeout-Ms": "15000"
+  }
+}
+```
+
+Expected Envoy logs:
+
+```console
+[...] wasm log http_auth_random: Access granted.
+```