External authorization (ext_authz) filter

This sandbox demonstrates Envoy’s ext_authz filter capability to delegate authorization of incoming requests through Envoy to an external services.

While ext_authz can also be employed as a network filter, this sandbox is limited to demonstrating the ext_authz HTTP filter, which supports calling HTTP or gRPC services.

The setup of this sandbox is very similar to a front-proxy deployment, however calls to the upstream service behind the proxy will be checked by an external HTTP or gRPC service. In this sandbox, for every authorized call, the external authorization service adds an additional x-current-user header to the headers forwarded to the upstream service.

Step 1: Start all of our containers

Change to the ext_authz directory.

To build this sandbox example and start the example services, run the following commands:

$ pwd
examples/ext_authz
$ docker compose pull
$ docker compose up --build -d
$ docker compose ps

               Name                             Command               State                   Ports
--------------------------------------------------------------------------------------------------------------------
ext_authz_ext_authz-grpc-service_1   /app/server -users /etc/us       Up
ext_authz_ext_authz-http-service_1   docker-entrypoint.sh node        Up
ext_authz_front-envoy_1              /docker-entrypoint.sh /bin       Up           10000/tcp, 0.0.0.0:8000->8000/tcp
ext_authz_upstream-service_1         python3 /code/service.py         Up (healthy)

Note

This sandbox has multiple configurations set up. The configuration is controlled by thge FRONT_ENVOY_YAML environment variable when selecting the Envoy configuration to be used. The default value of FRONT_ENVOY_YAML can be defined in the .env file or provided inline when running the docker compose up command.

For more information, please take a look at environment variables in Compose documentation.

By default, FRONT_ENVOY_YAML points to config/grpc-service/v3.yaml file which bootstraps front-envoy with ext_authz HTTP filter with gRPC service V3 (this is specified by transport_api_version field).

The possible values of FRONT_ENVOY_YAML can be found inside the config directory.

For example, to run Envoy with ext_authz HTTP filter with HTTP service will be:

$ pwd
examples/ext_authz
$ docker compose pull
$ # Tearing down the currently running setup
$ docker compose down
$ FRONT_ENVOY_YAML=config/http-service.yaml docker compose up --build -d
$ # Or you can update the .env file with the above FRONT_ENVOY_YAML value, so you don't have to specify it when running the "up" command.

Step 4: Access the upstream-service behind the Front Envoy

You can now try to send a request to upstream-service via the front Envoy as follows:

$ curl -v localhost:8000/service
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /service HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.58.0
> Accept: */*
>
< HTTP/1.1 403 Forbidden
< date: Fri, 19 Jun 2020 15:02:24 GMT
< server: envoy
< content-length: 0

As observed, the request failed with 403 Forbidden status code. This happened since the ext_authz filter employed by Envoy rejected the call. To let the request reach the upstream service, you need to provide a Bearer token via the Authorization header.

Note

A complete list of users is defined in auth/users.json file. For example, the token1 used in the below example is corresponding to user1.

An example of successful requests can be observed as follows:

$ curl -v -H "Authorization: Bearer token1" localhost:8000/service
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8000 (#0)
> GET /service HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.58.0
> Accept: */*
> Authorization: Bearer token1
>
< HTTP/1.1 200 OK
< content-type: text/html; charset=utf-8
< content-length: 24
< server: envoy
< date: Fri, 19 Jun 2020 15:04:29 GMT
< x-envoy-upstream-service-time: 2
<
* Connection #0 to host localhost left intact
Hello user1 from behind Envoy!

We can also employ Open Policy Agent server (with envoy_ext_authz_grpc plugin enabled) as the authorization server. To run this example:

$ pwd
examples/ext_authz
$ docker compose pull
$ # Tearing down the currently running setup
$ docker compose down
$ FRONT_ENVOY_YAML=config/opa-service/v3.yaml docker compose up --build -d

And sending a request to the upstream service (via the Front Envoy) gives:

$ curl localhost:8000/service --verbose
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8000 (#0)
> GET /service HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: text/html; charset=utf-8
< content-length: 28
< server: envoy
< date: Thu, 02 Jul 2020 06:29:58 GMT
< x-envoy-upstream-service-time: 2
<
* Connection #0 to host localhost left intact
Hello OPA from behind Envoy!

From the logs, we can observe the policy decision message from the Open Policy Agent (OPA) server (for the above request against the defined policy in config/opa-service/policy.rego):

$ docker compose logs ext_authz-opa-service | grep decision_id -A 30
ext_authz-opa-service_1   |   "decision_id": "8143ca68-42d8-43e6-ade6-d1169bf69110",
ext_authz-opa-service_1   |   "input": {
ext_authz-opa-service_1   |     "attributes": {
ext_authz-opa-service_1   |       "destination": {
ext_authz-opa-service_1   |         "address": {
ext_authz-opa-service_1   |           "Address": {
ext_authz-opa-service_1   |             "SocketAddress": {
ext_authz-opa-service_1   |               "PortSpecifier": {
ext_authz-opa-service_1   |                 "PortValue": 8000
ext_authz-opa-service_1   |               },
ext_authz-opa-service_1   |               "address": "172.28.0.6"
ext_authz-opa-service_1   |             }
ext_authz-opa-service_1   |           }
ext_authz-opa-service_1   |         }
ext_authz-opa-service_1   |       },
ext_authz-opa-service_1   |       "metadata_context": {},
ext_authz-opa-service_1   |       "request": {
ext_authz-opa-service_1   |         "http": {
ext_authz-opa-service_1   |           "headers": {
ext_authz-opa-service_1   |             ":authority": "localhost:8000",
ext_authz-opa-service_1   |             ":method": "GET",
ext_authz-opa-service_1   |             ":path": "/service",
ext_authz-opa-service_1   |             "accept": "*/*",
ext_authz-opa-service_1   |             "user-agent": "curl/7.64.1",
ext_authz-opa-service_1   |             "x-forwarded-proto": "http",
ext_authz-opa-service_1   |             "x-request-id": "b77919c0-f1d4-4b06-b444-5a8b32d5daf4"
ext_authz-opa-service_1   |           },
ext_authz-opa-service_1   |           "host": "localhost:8000",
ext_authz-opa-service_1   |           "id": "16617514055874272263",
ext_authz-opa-service_1   |           "method": "GET",
ext_authz-opa-service_1   |           "path": "/service",

Trying to send a request with method other than GET gives a rejection:

$ curl -X POST localhost:8000/service --verbose
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8000 (#0)
> PUT /service HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 403 Forbidden
< date: Thu, 02 Jul 2020 06:46:13 GMT
< server: envoy
< content-length: 0