Envoy WASM with external gRPC server

2020-12-20

Sample for envoy with WASM filter where the filter will invoke an external GRPC service.

THe full flow is like this:

client -> 

    (jwt_header) -> 
      [ 
        envoy.filters.network.http_connection_manager ->
        envoy.filters.http.jwt_authn ->
        envoy.filters.http.wasm ->
      ]
      -> (api_req) -> (jwt_header) gRPC server -> (api_resp)
                                                            -> [
                                                                 envoy.filters.http.router
                                                               ] 
                                                                 -> upstream_server

Basically, the client transmits a jwt bearer authorization token to envoy. Envoy will first validate the JWT header using its native jwt_authn filter Once validated, the decoded JWT claims are emitted as metadata to a wasm filter The wasm filter will extract the sub field metadata and use that in an rpc call to an external gRPC server. The external grpcServer will respond back isAdmin: true if the sub field is Alice, otherwise the value is false. Envoy will ultimately send the isAdmin header to the upstream server. The upstream server is httpbin.org which will just display the headers it received.

This flow is very similar to how external authorization servers can be configured (shown below). However, this repo is just a sample which demonstrates how to configure/develop an filter.

I’ve done building the wasm filter the hard way…you should consider just taking a look at wasme

The sample filter is also just a copy of the wasm-cc sandbox filter

References:

To use this sample, you’ll need:

docker cp `docker create envoyproxy/envoy-dev:latest`:/usr/local/bin/envoy /tmp/

/tmp/envoy --version
   version: 27c507ee0ae51713dbdf66a24cb9a47f46700b78/1.20.0-dev/Clean/RELEASE/BoringSSL
  • golang 1.17
  • optional protoc

You can find the source here


Setup

Build wasm filter

First clone envoy and build the filter

git clone https://github.com/envoyproxy/envoy.git
rm -rf envoy/examples/wasm-cc/
cp -R wasm-cc envoy/examples

Now build the modified filter

cd envoy 
bazel build //examples/wasm-cc:envoy_filter_http_wasm_example.wasm

Host override

Add to /etc/hosts

127.0.0.1	grpc.domain.com

This is the address for the grpc server (this is just for convenience to make the SNI match

(you don’t need to do this but i got lazy with the envoy config…TODO: configure envoy better)

Run Envoy

/tmp/envoy -c envoy-wasm.yaml -l debug

Run gRPC Server

cd grpc_server/

# (optional) recompile protos
# /usr/local/bin/protoc --go_out=. --go_opt=paths=source_relative  --descriptor_set_out=echo/echo.proto.pb   --go-grpc_out=. --go-grpc_opt=paths=source_relative     echo/echo.proto

# run server
go run greeter_server/grpc_server.go --tlsCert grpc_server_crt.pem --tlsKey grpc_server_key.pem --grpcport :50051

## test client
# go run greeter_client/grpc_client.go  --host localhost:50051 --servername grpc.domain.com --cacert ../certs/tls-ca.crt

Run CLient

We’re going to use curl to emit two different pregenerated JWTs

Alice’s JWT includes her name in the sub field

{
  "alg": "RS256",
  "kid": "DHFbpoIUqrY8t2zpA2qXfCmr5VO5ZEr4RzHU_-envvQ",
  "typ": "JWT"
}.
{
  "exp": 1609408793,
  "iat": 1609108793,
  "iss": "new-issuer@secure.istio.io",
  "sub": "alice@domain.com"
}

And bob includes his

{
  "alg": "RS256",
  "kid": "DHFbpoIUqrY8t2zpA2qXfCmr5VO5ZEr4RzHU_-envvQ",
  "typ": "JWT"
}.
{
  "exp": 1609408787,
  "iat": 1609108787,
  "iss": "new-issuer@secure.istio.io",
  "sub": "bob@domain.com"
}

Now use their names to invoke

You can generate your own JWTs using istio’s handy scripts here:

wget --no-verbose https://raw.githubusercontent.com/istio/istio/release-1.10/security/tools/jwt/samples/gen-jwt.py
wget --no-verbose https://raw.githubusercontent.com/istio/istio/release-1.10/security/tools/jwt/samples/key.pem
python3 gen-jwt.py -iss foo.bar -aud sal -expire 100000 key.pem
JWK URI = "https://raw.githubusercontent.com/istio/istio/release-1.10/security/tools/jwt/samples/jwks.json";
  • Alice
curl -v -H "host: http.domain.com"  --resolve  http.domain.com:8080:127.0.0.1 \
  -H "Authorization: Bearer `cat jwts/alice.txt`" \
  -H "User: sal" http://http.domain.com:8080/get


> GET /get HTTP/1.1
> Host: http.domain.com
> User-Agent: curl/7.72.0
> Accept: */*
> Authorization: Bearer eyJhbGciOiJSUzI1NiIsImtpZCI6IkRIRmJwb0lVcXJZOHQyenBBMnFYZkNtcjVWTzVaRXI0UnpIVV8tZW52dlEiLCJ0eXAiOiJKV1QifQ.eyJleHAiOjE2MDk0MDg3OTMsImlhdCI6MTYwOTEwODc5MywiaXNzIjoibmV3LWlzc3VlckBzZWN1cmUuaXN0aW8uaW8iLCJzdWIiOiJhbGljZUBkb21haW4uY29tIn0.WeRcHxVsKZAKD1uu-1efYhUwH9K5cWr6-Doo-CVulAhPol8oXazmZ-6wMUnqtOcWh5YOevVzUhIF8jUDibIHgsvksSprXrZf8BAkC68ctb1O0eDTlhKw0fdS41PedmBWnTESkBYFgEAKDeS4Re3bIN2irPVfSTldxqXepkl8K6R_R_Gnuyqxaie16JmIADMJ1unRbd4rcW3grXdYF4Dc7EvCpinQuQJQOdaNn1mQ2JrckTnrr8R6xf6pLpEDjAKGqeNKQdRjAAUdHSZqIylHMwIgcWAVrTFWz9TmUrmQmSqReJRa4SdAGBaTCKL9UeBiqyGYpEZn1wCfMj-ukwNQvA
> User: sal

< HTTP/1.1 200 OK
< date: Mon, 28 Dec 2020 00:55:39 GMT
< server: envoy
< access-control-allow-origin: *
< access-control-allow-credentials: true
< x-envoy-upstream-service-time: 34
< x-wasm-custom: FOO
< content-type: text/plain; charset=utf-8
< transfer-encoding: chunked

{
  "args": {}, 
  "headers": {
    "Accept": "*/*", 
    "Content-Length": "0", 
    "Host": "http.domain.com", 
    "Isadmin": "true", 
    "User": "sal", 
    "User-Agent": "curl/7.72.0", 
    "X-Amzn-Trace-Id": "Root=1-5fe92d0b-079e277b0d79542f3c3e7af6", 
    "X-Envoy-Expected-Rq-Timeout-Ms": "15000"
  }, 
  "origin": "69.250.44.79", 
  "url": "http://http.domain.com/get"
}

Hello, world

The authorization bearer token is the client token Alice sends.

  • "Isadmin": "true": the auth header is decoded by envoy. The sub field is given to the gRPC server. If the sub=Alice, then the gRPC server adds this header back in the response. The wasm filter will append isAdmin:true to the upstram.

  • x-wasm-custom: FOO: this is a header value the wasm filter returns back to the client.

  • Bob

If bob tries to use his jwt token in the same way, the header he sees is isAdmin: false

curl -v -H "host: http.domain.com"  --resolve  http.domain.com:8080:127.0.0.1 \
  -H "Authorization: Bearer `cat jwts/bob.txt`" \
  -H "User: sal" http://http.domain.com:8080/get


> GET /get HTTP/1.1
> Host: http.domain.com
> User-Agent: curl/7.72.0
> Accept: */*
> Authorization: Bearer eyJhbGciOiJSUzI1NiIsImtpZCI6IkRIRmJwb0lVcXJZOHQyenBBMnFYZkNtcjVWTzVaRXI0UnpIVV8tZW52dlEiLCJ0eXAiOiJKV1QifQ.eyJleHAiOjE2MDk0MDg3ODcsImlhdCI6MTYwOTEwODc4NywiaXNzIjoibmV3LWlzc3VlckBzZWN1cmUuaXN0aW8uaW8iLCJzdWIiOiJib2JAZG9tYWluLmNvbSJ9.Q3QPnOkqhQN_BrDDmmSpugLRVbcyoXrXgl7NqtlUrZeef2tMQh7ycJhg4z73J6iw49v7ye2CgMrjScHTUVaGgPItItYAVfTwGXC-VBekqnrhCRhZ57ou3vJHjT7xADL9qvwahBDKjpGji8uzsvHsHZXBgiVxVh_5lYBLt6PcoVgqHAgn_uNTnE0EJJgV7Vs39k73wtxqYkuvpZdMdaWw1gLOmFhxSu2yqLHNtfLZIPyVZxyrK1KtAw9yFIDmsIEtLOpjdIqKIJ5Nh48OeN5LNhz0r2Alrj7nM_d11FYc-0k9R58vRE7SgIJNvzUKlcptkjHb0K23DoIw8QnhFFHGfg
> User: sal

< HTTP/1.1 200 OK
< date: Mon, 28 Dec 2020 01:01:31 GMT
< server: envoy
< access-control-allow-origin: *
< access-control-allow-credentials: true
< x-envoy-upstream-service-time: 41
< x-wasm-custom: FOO
< content-type: text/plain; charset=utf-8
< transfer-encoding: chunked

{
  "args": {}, 
  "headers": {
    "Accept": "*/*", 
    "Content-Length": "0", 
    "Host": "http.domain.com", 
    "Isadmin": "false", 
    "User": "sal", 
    "User-Agent": "curl/7.72.0", 
    "X-Amzn-Trace-Id": "Root=1-5fe92e6b-47819b1739fd76e15353398b", 
    "X-Envoy-Expected-Rq-Timeout-Ms": "15000"
  }, 
  "origin": "69.250.44.79", 
  "url": "http://http.domain.com/get"
}

Hello, world

A couple of notes about the flow:

  • envoy.filters.network.http_connection_manager will remove the isAdmin header if its sent in unilaterally by the client. see internal_only_headers: - isadmin setting

  • envoy.filters.http.jwt_authn will validate the inboud jwt and emit the claims as dynamic metadata see payload_in_metadata: "my_payload"

  • envoy.filters.http.wasm will read the config file for the gRPC cluster name:

                      configuration:
                     "@type": "type.googleapis.com/google.protobuf.StringValue"
                     value: |
                       {
                        "clustername": "grpc.domain.com",
                       } 
    

    the configuration file is actually defined as a proto struct here: wasm-cc/echo/echo.proto:

          // this proto represents configuration for the example filter
          message Config {
            string clustername = 1;
          }
    

    The proto messages the wasm filter uses to make the outbound call is also defined and compiled with the wasm filter. see wasm-cc/echo/echo.proto

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