opa

Summary

• Description
• Attributes
• Data Definition
• Example

Description

The opa plugin is used to integrate with Open Policy Agent. By using this plugin, users can decouple functions such as authentication and access to services and reduce the complexity of the application system.

Attributes

Data Definition

APISIX to OPA service

The type indicates that the request type. (e.g. http or stream) The reqesut is used when the request type is http, it contains the basic information of the request. (e.g. url, header) The var contains basic information about this requested connection. (e.g. IP, port, request timestamp) The route, service, and consumer will be sent only after the opa plugin has enabled the relevant features, and their contents are same as those stored by APISIX in etcd.

{
    "type": "http",
    "request": {
        "scheme": "http",
        "path": "\/get",
        "headers": {
            "user-agent": "curl\/7.68.0",
            "accept": "*\/*",
            "host": "127.0.0.1:9080"
        },
        "query": {},
        "port": 9080,
        "method": "GET",
        "host": "127.0.0.1"
    },
    "var": {
        "timestamp": 1701234567,
        "server_addr": "127.0.0.1",
        "server_port": "9080",
        "remote_port": "port",
        "remote_addr": "ip address"
    },
    "route": {},
    "service": {},
    "consumer": {}
}

OPA service response to APISIX

In the response, result is automatically added by OPA. The allow is indispensable and will indicate whether the request is allowed to be forwarded through the APISIX. The reason, headers, and status_code are optional and are only returned when you need to use a custom response, as you’ll see in the next section with the actual use case for it.

{
    "result": {
        "allow": true,
        "reason": "test",
        "headers": {
            "an": "header"
        },
        "status_code": 401
    }
}

Example

First, you need to launch the Open Policy Agent environment.

$ docker run -d --name opa -p 8181:8181 openpolicyagent/opa:0.35.0 run -s

Basic Use Case

You can create a basic policy for testing.

$ curl -X PUT '127.0.0.1:8181/v1/policies/example1' \
    -H 'Content-Type: text/plain' \
    -d 'package example1
import input.request
default allow = false
allow {
    # HTTP method must GET
    request.method == "GET"
}'

After that, you can create a route and turn on the opa plugin.

$ curl -X PUT 'http://127.0.0.1:9080/apisix/admin/routes/r1' \
    -H 'X-API-KEY: <api-key>' \
    -H 'Content-Type: application/json' \
    -d '{
    "uri": "/*",
    "plugins": {
        "opa": {
            "host": "http://127.0.0.1:8181",
            "policy": "example1"
        }
    },
    "upstream": {
        "nodes": {
            "httpbin.org:80": 1
        },
        "type": "roundrobin"
    }
}'

Try it out.

# Successful request
$ curl -i -X GET 127.0.0.1:9080/get
HTTP/1.1 200 OK
# Failed request
$ curl -i -X POST 127.0.0.1:9080/post
HTTP/1.1 403 FORBIDDEN

Complex Use Case (custom response)

Next, let’s think about some more complex scenarios.

When you need to return a custom error message for an incorrect request, you can implement it this way.

$ curl -X PUT '127.0.0.1:8181/v1/policies/example2' \
    -H 'Content-Type: text/plain' \
    -d 'package example2
import input.request
default allow = false
allow {
    request.method == "GET"
}
# custom response body (Accepts a string or an object, the object will respond as JSON format)
reason = "test" {
    not allow
}
# custom response header (The data of the object can be written in this way)
headers = {
    "Location": "http://example.com/auth"
} {
    not allow
}
# custom response status code
status_code = 302 {
    not allow
}'

Update the route and set opa plugin’s policy parameter to example2. Then, let’s try it.

# Successful request
$ curl -i -X GET 127.0.0.1:9080/get
HTTP/1.1 200 OK
# Failed request
$ curl -i -X POST 127.0.0.1:9080/post
HTTP/1.1 302 FOUND
Location: http://example.com/auth
test

Complex Use Case (send APISIX data)

Let’s think about another scenario, when your decision needs to use some APISIX data, such as route, consumer, etc., how should we do it?

Create a simple policy echo, which will return the data sent by APISIX to the OPA service as is, so we can simply see them.

$ curl -X PUT '127.0.0.1:8181/v1/policies/echo' \
    -H 'Content-Type: text/plain' \
    -d 'package echo
allow = false
reason = input'

Next, update the config of the route to enable sending route data.

$ curl -X PUT 'http://127.0.0.1:9080/apisix/admin/routes/r1' \
    -H 'X-API-KEY: <api-key>' \
    -H 'Content-Type: application/json' \
    -d '{
    "uri": "/*",
    "plugins": {
        "opa": {
            "host": "http://127.0.0.1:8181",
            "policy": "echo",
            "with_route": true
        }
    },
    "upstream": {
        "nodes": {
            "httpbin.org:80": 1
        },
        "type": "roundrobin"
    }
}'

Try it. As you can see, we output this data with the help of the custom response body function described above, along with the data from the route.

$ curl -X GET 127.0.0.1:9080/get
{
    "type": "http",
    "request": {
        xxx
    },
    "var": {
        xxx
    },
    "route": {
        xxx
    }
}