Validate incoming JSON request bodies with JSON Threat Protection

Uses: Kong Gateway decK

Deployment Platform:

Prerequisites

Kong Konnect

This is a Konnect tutorial. If you don’t have a Konnect account, you can get started quickly with our onboarding wizard.

The following Konnect items are required to complete this tutorial:
- Personal access token (PAT): Create a new personal access token by opening the Konnect PAT page and selecting Generate Token.
- Control Plane Name: You can use an existing Control Plane or create a new one to use for this tutorial.
- Konnect Proxy URL: By default, a self-hosted Data Plane uses http://localhost:8000. You can set up Data Plane nodes for your Control Plane from the Gateway Manager in Konnect.

Set the personal access token, the Control Plane name, the Control Plane URL, and the Konnect proxy URL as environment variables:

 export DECK_KONNECT_TOKEN='YOUR KONNECT TOKEN'
 export DECK_KONNECT_CONTROL_PLANE_NAME='YOUR CONTROL PLANE NAME'
 export KONNECT_CONTROL_PLANE_URL=https://us.api.konghq.com
 export KONNECT_PROXY_URL='KONNECT PROXY URL'

Kong Gateway running

This tutorial requires Kong Gateway Enterprise. If you don’t have Kong Gateway set up yet, you can use the quickstart script with an enterprise license to get an instance of Kong Gateway running almost instantly.

Export your license to an environment variable:

 export KONG_LICENSE_DATA='LICENSE-CONTENTS-GO-HERE'

Run the quickstart script:

 curl -Ls https://get.konghq.com/quickstart | bash -s -- -e KONG_LICENSE_DATA 

Once Kong Gateway is ready, you will see the following message:

 Kong Gateway Ready

decK

decK is a CLI tool for managing Kong Gateway declaratively with state files. To complete this tutorial you will first need to install decK.

Required entities

For this tutorial, you’ll need Kong Gateway entities, like Gateway Services and Routes, pre-configured. These entities are essential for Kong Gateway to function but installing them isn’t the focus of this guide. Follow these steps to pre-configure them:

Run the following command:

echo '
_format_version: "3.0"
services:
  - name: example-service
    url: http://httpbin.konghq.com/anything
routes:
  - name: example-route
    paths:
    - "/anything"
    service:
      name: example-service
' | deck gateway apply -

To learn more about entities, you can read our entities documentation.

Create a JSON threat protection policy

Configure the JSON Threat Protection plugin on the example-route Route to set limits on the contents of incoming request bodies.

In the following example, we enable the plugin in block mode, which will reject any requests that don’t conform to the policy, and instead respond with a 400 error and the message Incorrect request format:

echo '
_format_version: "3.0"
plugins:
  - name: json-threat-protection
    route: example-route
    config:
      max_body_size: 1024
      max_container_depth: 2
      max_object_entry_count: 4
      max_object_entry_name_length: 7
      max_array_element_count: 2
      max_string_value_length: 6
      enforcement_mode: block
      error_status_code: 400
      error_message: Incorrect request format
' | deck gateway apply -

Validate the policy

Let’s make a valid request. The following request conforms to the policy that we just created:

curl -i -X POST "$KONNECT_PROXY_URL/anything" \
     -H "Content-Type: application/json" \
     --json '{
       "name": "Jason",
       "age": 20,
       "gender": "male",
       "parents": [
         "Joseph",
         "Viva"
       ]
     }'

curl -i -X POST "http://localhost:8000/anything" \
     -H "Content-Type: application/json" \
     --json '{
       "name": "Jason",
       "age": 20,
       "gender": "male",
       "parents": [
         "Joseph",
         "Viva"
       ]
     }'

You should get a 200 response, and the request gets proxied to the upstream service.

Now, try a request with a payload that doesn’t conform to the policy:

curl -i -X POST "$KONNECT_PROXY_URL/anything" \
     -H "Content-Type: application/json" \
     --json '{
       "name": "Jason",
       "age": 20,
       "gender": "male",
       "parents": [
         "Antonio",
         "Viva"
       ]
     }'

curl -i -X POST "http://localhost:8000/anything" \
     -H "Content-Type: application/json" \
     --json '{
       "name": "Jason",
       "age": 20,
       "gender": "male",
       "parents": [
         "Antonio",
         "Viva"
       ]
     }'

In this case, the string Antonio is longer than the maximum allowed string length of 6, so the request is blocked. The plugin returns a 400 response and the message Incorrect request format.

Cleanup

Clean up Konnect environment

If you created a new control plane and want to conserve your free trial credits or avoid unnecessary charges, delete the new control plane used in this tutorial.

Destroy the Kong Gateway container

curl -Ls https://get.konghq.com/quickstart | bash -s -- -d

FAQs

How can I enable a JSON threat protection policy without blocking non-conforming requests?

You can enable the JSON Threat Protection plugin in tap mode by setting config.enforcement_mode to log_only. In tap mode, the plugin still inspects the JSON body but only logs warnings instead of blocking violations, and still proxies the request to the upstream service.