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Request Transformer Advanced

Transform client requests before they reach the upstream server. The plugin lets you match portions of incoming requests using regular expressions, save those matched strings into variables, and substitute the strings into transformed requests via flexible templates.

The Request Transformer Advanced plugin builds on the open-source Request Transformer plugin with the following enhanced capability:

  • Limit the list of allowed parameters in the request body. Set this up with the allow.body configuration parameter.

Configuration Reference

This plugin is compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

  • Setting a target's health status in the load balancer
  • Validating configurations against schemas
  • Uploading the declarative configuration using the /config endpoint

Example plugin configuration

The following examples provide some typical configurations for enabling the request-transformer-advanced plugin on a service.

Make the following request:

curl -X POST http://localhost:8001/services/SERVICE_NAME|SERVICE_ID/plugins \
    --data "name=request-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.querystring=qs-old-name:qs-new-name" \
    --data "config.remove.querystring=qs2-old-name:qs2-new-name" \
    --data "config.remove.body=formparam-toremove" \
    --data "config.remove.body=formparam-another-one" \
    --data "config.replace.body=body-param1:new-value-1" \
    --data "config.replace.body=body-param2:new-value-2" \
    --data "config.rename.headers=header-old-name:header-new-name" \
    --data "config.rename.headers=another-old-name:another-new-name" \
    --data "config.rename.querystring=qs-old-name:qs-new-name" \
    --data "config.rename.querystring=qs2-old-name:qs2-new-name" \
    --data "config.rename.body=param-old:param-new" \
    --data "config.rename.body=param2-old:param2-new" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.querystring=new-param:some_value" \
    --data "config.add.querystring=another-param:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number"

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: request-transformer-advanced-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  remove:
    body:
    - formparam-toremove
    - formparam-another-one
  replace:
    body:
    - body-param1:new-value-1
    - body-param2:new-value-2
  rename:
    headers:
    - header-old-name:header-new-name
    - another-old-name:another-new-name
  rename:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  rename:
    body:
    - param-old:param-new
    - param2-old:param2-new
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    querystring:
    - new-param:some_value
    - another-param:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
plugin: request-transformer-advanced

Next, apply the KongPlugin resource to a service by annotating the service as follows:

apiVersion: v1
kind: Service
metadata:
  name: SERVICE_NAME|SERVICE_ID
  labels:
    app: SERVICE_NAME|SERVICE_ID
  annotations:
    konghq.com/plugins: request-transformer-advanced-example
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: SERVICE_NAME|SERVICE_ID
  selector:
    app: SERVICE_NAME|SERVICE_ID

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: request-transformer-advanced
  service: SERVICE_NAME|SERVICE_ID
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    remove:
      body:
      - formparam-toremove
      - formparam-another-one
    replace:
      body:
      - body-param1:new-value-1
      - body-param2:new-value-2
    rename:
      headers:
      - header-old-name:header-new-name
      - another-old-name:another-new-name
    rename:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    rename:
      body:
      - param-old:param-new
      - param2-old:param2-new
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      querystring:
      - new-param:some_value
      - another-param:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. From the Services section, click View for the service row.
  3. From the plugin section, click Add Plugin.
  4. Find and select the Request Transformer Advanced plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  5. If the option is available, select Scoped.
  6. Add the service name and ID to the Service field if it is not already pre-filled.
  7. Click Create.

The following examples provide some typical configurations for enabling the request-transformer-advanced plugin on a route.

Make the following request:

curl -X POST http://localhost:8001/routes/ROUTE_NAME|ROUTE_ID/plugins \
  --data "name=request-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.querystring=qs-old-name:qs-new-name" \
    --data "config.remove.querystring=qs2-old-name:qs2-new-name" \
    --data "config.remove.body=formparam-toremove" \
    --data "config.remove.body=formparam-another-one" \
    --data "config.replace.body=body-param1:new-value-1" \
    --data "config.replace.body=body-param2:new-value-2" \
    --data "config.rename.headers=header-old-name:header-new-name" \
    --data "config.rename.headers=another-old-name:another-new-name" \
    --data "config.rename.querystring=qs-old-name:qs-new-name" \
    --data "config.rename.querystring=qs2-old-name:qs2-new-name" \
    --data "config.rename.body=param-old:param-new" \
    --data "config.rename.body=param2-old:param2-new" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.querystring=new-param:some_value" \
    --data "config.add.querystring=another-param:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number"

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: request-transformer-advanced-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  remove:
    body:
    - formparam-toremove
    - formparam-another-one
  replace:
    body:
    - body-param1:new-value-1
    - body-param2:new-value-2
  rename:
    headers:
    - header-old-name:header-new-name
    - another-old-name:another-new-name
  rename:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  rename:
    body:
    - param-old:param-new
    - param2-old:param2-new
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    querystring:
    - new-param:some_value
    - another-param:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
plugin: request-transformer-advanced

Then, apply it to an ingress (route or routes) by annotating the ingress as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ROUTE_NAME|ROUTE_ID
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: request-transformer-advanced-example
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          service:
            name: echo
            port:
              number: 80

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: request-transformer-advanced
  route: ROUTE_NAME
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    remove:
      body:
      - formparam-toremove
      - formparam-another-one
    replace:
      body:
      - body-param1:new-value-1
      - body-param2:new-value-2
    rename:
      headers:
      - header-old-name:header-new-name
      - another-old-name:another-new-name
    rename:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    rename:
      body:
      - param-old:param-new
      - param2-old:param2-new
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      querystring:
      - new-param:some_value
      - another-param:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. Open Routes from the menu, then click View for the route row.
  3. From the plugin section, click Add Plugin.
  4. Find and select the Request Transformer Advanced plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  5. If the option is available, select Scoped.
  6. Add the route ID if it is not already prefilled.
  7. Click Create.

The following examples provide some typical configurations for enabling the request-transformer-advanced plugin on a consumer.

Make the following request:

curl -X POST http://localhost:8001/consumers/CONSUMER_NAME|CONSUMER_ID/plugins \
  --data "name=request-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.querystring=qs-old-name:qs-new-name" \
    --data "config.remove.querystring=qs2-old-name:qs2-new-name" \
    --data "config.remove.body=formparam-toremove" \
    --data "config.remove.body=formparam-another-one" \
    --data "config.replace.body=body-param1:new-value-1" \
    --data "config.replace.body=body-param2:new-value-2" \
    --data "config.rename.headers=header-old-name:header-new-name" \
    --data "config.rename.headers=another-old-name:another-new-name" \
    --data "config.rename.querystring=qs-old-name:qs-new-name" \
    --data "config.rename.querystring=qs2-old-name:qs2-new-name" \
    --data "config.rename.body=param-old:param-new" \
    --data "config.rename.body=param2-old:param2-new" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.querystring=new-param:some_value" \
    --data "config.add.querystring=another-param:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number"

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

You can combine consumer.id, service.id, or route.id in the same request, to further narrow the scope of the plugin.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: request-transformer-advanced-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  remove:
    body:
    - formparam-toremove
    - formparam-another-one
  replace:
    body:
    - body-param1:new-value-1
    - body-param2:new-value-2
  rename:
    headers:
    - header-old-name:header-new-name
    - another-old-name:another-new-name
  rename:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  rename:
    body:
    - param-old:param-new
    - param2-old:param2-new
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    querystring:
    - new-param:some_value
    - another-param:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
plugin: request-transformer-advanced

Then, apply it to a consumer by annotating the KongConsumer resource as follows:

apiVersion: configuration.konghq.com/v1
kind: KongConsumer
metadata:
  name: CONSUMER_NAME|CONSUMER_ID
  annotations:
    konghq.com/plugins: request-transformer-advanced-example
    kubernetes.io/ingress.class: kong

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: request-transformer-advanced
  consumer: CONSUMER_NAME|CONSUMER_ID
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    remove:
      body:
      - formparam-toremove
      - formparam-another-one
    replace:
      body:
      - body-param1:new-value-1
      - body-param2:new-value-2
    rename:
      headers:
      - header-old-name:header-new-name
      - another-old-name:another-new-name
    rename:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    rename:
      body:
      - param-old:param-new
      - param2-old:param2-new
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      querystring:
      - new-param:some_value
      - another-param:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. From the Consumers section, click View for the consumer row.
  3. Select the Plugins tab, then click Add Plugin.
  4. Find and select the Request Transformer Advanced plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  5. If the option is available, select Scoped.
  6. Add the consumer ID if it is not already prefilled.
  7. Click Create.

A plugin which is not associated to any service, route, or consumer is considered global, and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

The following examples provide some typical configurations for enabling the request-transformer-advanced plugin globally.

Make the following request:

curl -X POST http://localhost:8001/plugins/ \
  --data "name=request-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.querystring=qs-old-name:qs-new-name" \
    --data "config.remove.querystring=qs2-old-name:qs2-new-name" \
    --data "config.remove.body=formparam-toremove" \
    --data "config.remove.body=formparam-another-one" \
    --data "config.replace.body=body-param1:new-value-1" \
    --data "config.replace.body=body-param2:new-value-2" \
    --data "config.rename.headers=header-old-name:header-new-name" \
    --data "config.rename.headers=another-old-name:another-new-name" \
    --data "config.rename.querystring=qs-old-name:qs-new-name" \
    --data "config.rename.querystring=qs2-old-name:qs2-new-name" \
    --data "config.rename.body=param-old:param-new" \
    --data "config.rename.body=param2-old:param2-new" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.querystring=new-param:some_value" \
    --data "config.add.querystring=another-param:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number"

Create a KongClusterPlugin resource and label it as global:

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-request-transformer-advanced>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  remove:
    body:
    - formparam-toremove
    - formparam-another-one
  replace:
    body:
    - body-param1:new-value-1
    - body-param2:new-value-2
  rename:
    headers:
    - header-old-name:header-new-name
    - another-old-name:another-new-name
  rename:
    querystring:
    - qs-old-name:qs-new-name
    - qs2-old-name:qs2-new-name
  rename:
    body:
    - param-old:param-new
    - param2-old:param2-new
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    querystring:
    - new-param:some_value
    - another-param:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
plugin: request-transformer-advanced

Add a plugins entry in the declarative configuration file:

plugins:
- name: request-transformer-advanced
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    remove:
      body:
      - formparam-toremove
      - formparam-another-one
    replace:
      body:
      - body-param1:new-value-1
      - body-param2:new-value-2
    rename:
      headers:
      - header-old-name:header-new-name
      - another-old-name:another-new-name
    rename:
      querystring:
      - qs-old-name:qs-new-name
      - qs2-old-name:qs2-new-name
    rename:
      body:
      - param-old:param-new
      - param2-old:param2-new
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      querystring:
      - new-param:some_value
      - another-param:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. Open Plugins from the menu, then click New Plugin.
  3. Find and select the Request Transformer Advanced plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  4. If the option is available, set the plugin scope to Global.
  5. Click Create.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Form Parameter Description
name

required

Type: string

 The name of the plugin, in this case request-transformer-advanced.
instance_name

optional

Type: string

An optional custom name to identify an instance of the plugin, for example request-transformer-advanced_my-service.

Useful when running the same plugin in multiple contexts, for example, on multiple services.
service.name or service.id

optional

Type: string

The name or ID of the service the plugin targets.

Set one of these parameters if adding the plugin to a service through the top-level /plugins endpoint.

Not required if using /services/SERVICE_NAME|SERVICE_ID/plugins.
route.name or route.id

optional

Type: string

The name or ID of the route the plugin targets.

Set one of these parameters if adding the plugin to a route through the top-level /plugins endpoint.

Not required if using /routes/ROUTE_NAME|ROUTE_ID/plugins.
consumer.name or consumer.id

optional


Type: string

The name or ID of the consumer the plugin targets.

Set one of these parameters if adding the plugin to a consumer through the top-level /plugins endpoint.

Not required if using /consumers/CONSUMER_NAME|CONSUMER_ID/plugins.
enabled

optional

Type: boolean

Default value: true

 Whether this plugin will be applied.
config.http_method

optional

Type: string


Changes the HTTP method for the upstream request.
config.remove.headers

optional

Type: array of string elements


List of header names. Unset the headers with the given name.
config.remove.querystring

optional

Type: array of string elements


List of querystring names. Remove the querystring if it is present.
config.remove.body

optional

Type: array of string elements


List of parameter names. Remove the parameter if and only if content-type is one of the following: [application/json, multipart/form-data, application/x-www-form-urlencoded]; and parameter is present.
config.replace.headers

optional

Type: array of string elements


List of headername:value pairs. If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.replace.querystring

optional

Type: array of string elements


List of queryname:value pairs. If and only if the querystring name is already set, replace its old value with the new one. Ignored if the header is not already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.replace.uri

optional

Type: string


Updates the upstream request URI with given value. This value can only be used to update the path part of the URI; not the scheme, nor the hostname.
config.replace.body

optional

Type: array of string elements


List of paramname:value pairs. If and only if content-type is one the following: [application/json, multipart/form-data, application/x-www-form-urlencoded]; and the parameter is already present, replace its old value with the new one. Ignored if the parameter is not already present.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.replace.json_types

optional

Type: array of string, boolean, or number elements


List of JSON type names. Specify the types of the JSON values returned when replacing JSON properties.
config.rename.headers

optional

Type: array of string elements


List of headername:value pairs. If and only if the header is already set, rename the header. The value is unchanged. Ignored if the header is not already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.rename.querystring

optional

Type: array of string elements


List of queryname:value pairs. If and only if the field name is already set, rename the field name. The value is unchanged. Ignored if the field name is not already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.rename.body

optional

Type: array of string elements


List of parameter name:value pairs. Rename the parameter name if and only if content-type is one of the following: [application/json, multipart/form-data, application/x-www-form-urlencoded]; and parameter is present.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.add.headers

optional

Type: array of string elements


List of headername:value pairs. If and only if the header is not already set, set a new header with the given value. Ignored if the header is already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.add.querystring

optional

Type: array of string elements


List of queryname:value pairs. If and only if the querystring name is not already set, set a new querystring with the given value. Ignored if the querystring name is already set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.add.body

optional

Type: array of string elements


List of paramname:value pairs. If and only if content-type is one the following: [application/json, multipart/form-data, application/x-www-form-urlencoded]; and the parameter is not present, add a new parameter with the given value to form-encoded body. Ignored if the parameter is already present.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.add.json_types

optional

Type: array of string, boolean, or number elements


List of JSON type names. Specify the types of the JSON values returned when adding a new JSON property.
config.append.headers

optional

Type: array of string elements


List of headername:value pairs. If the header is not set, set it with the given value. If it is already set, a new header with the same name and the new value will be set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.append.querystring

optional

Type: array of string elements


List of queryname:value pairs. If the querystring is not set, set it with the given value. If it is already set, a new querystring with the same name and the new value will be set.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.append.body

optional

Type: array of string elements


List of paramname:value pairs. If the content-type is one the following: [application/json, application/x-www-form-urlencoded]; add a new parameter with the given value if the parameter is not present. Otherwise, if it is already present, the two values (old and new) will be aggregated in an array.

This field is referenceable, which means it can be securely stored as a secret in a vault. References must follow a specific format.

config.append.json_types

optional

Type: array of string, boolean, or number elements


List of JSON type names. Specify the types of the JSON values returned when appending JSON properties.
config.allow.body

optional

Type: array of string elements


Set of parameter names. If and only if content-type is one the following: [application/json, multipart/form-data, application/x-www-form-urlencoded]; allow only allowed parameters in the body.
config.dots_in_keys

optional

Type: boolean

Default value: true


Specify whether dots (for example, customers.info.phone) should be treated as part of a property name or used to descend into nested JSON objects. See Arrays and nested objects.

Notes:

  • If the value contains a , (comma), then the comma-separated format for lists cannot be used. The array notation must be used instead.
  • The X-Forwarded-* fields are non-standard header fields written by Nginx to inform the upstream about client details and can’t be overwritten by this plugin. If you need to overwrite these header fields, see the post-function plugin in Serverless Functions.

Template as Value

You can use any of the current request headers, query parameters, and captured URI groups as templates to populate supported config fields.

Request Parameter Template
header $(headers.<header-name>) or $(headers["<header-name>"]))
querystring $(query_params.<query-param-name>) or $(query_params["<query-param-name>"]))
captured URIs $(uri_captures.<group-name>) or $(uri_captures["<group-name>"]))

To escape a template, wrap it inside quotes and pass inside another template. For example:

$('$(something_that_needs_to_escaped)')

Note: The plugin creates a non-mutable table of request headers, query strings, and captured URIs before transformation. So any update or removal of parameters used in the template does not affect the rendered value of template.

Arrays and nested objects

The plugin allows navigating complex JSON objects (arrays and nested objects) when config.dots_in_keys is set to false (the default is true).

  • array[*]: Loops through all elements of the array.
  • array[N]: Navigates to the nth element of the array (the index of the first element is 1).
  • top.sub: Navigates to the sub property of the top object.

These can be combined. For example, config.remove.json: customers[*].info.phone removes all phone properties from inside the info object of all entries in the customers array.

Advanced templates

The content of the placeholder $(...) is evaluated as a Lua expression, so logical operators may be used. For example:

Header-Name:$(uri_captures["user-id"] or query_params["user"] or "unknown")

This will first look for the path parameter (uri_captures); if not found, it will return the query parameter; or if that also doesn’t exist, it returns the default value ‘“unknown”’.

Constant parts can be specified as part of the template outside the dynamic placeholders. For example, creating a basic-auth header from a query parameter called auth that only contains the base64-encoded part:

Authorization:Basic $(query_params["auth"])

Lambdas are also supported if wrapped as an expression like this:

$((function() ... implementation here ... end)())

A complete lambda example for prefixing a header value with “Basic “ if not already there:

Authorization:$((function()
    local value = headers.Authorization
    if not value then
      return
    end
    if value:sub(1, 6) == "Basic " then
      return value            -- was already properly formed
    end
    return "Basic " .. value  -- added proper prefix
  end)())

Note: Especially in multi-line templates like the example above, make sure not to add any trailing white-space or new-lines. Since these would be outside the placeholders, they would be considered part of the template, and hence would be appended to the generated value.

The environment is sandboxed, meaning that Lambda’s will not have access to any library functions, except for the string methods (like sub() in the example above).

Examples Using Template as Value

Add a Service named test which routes requests to the mockbin.com upstream service:

curl -X POST http://localhost:8001/services \
    --data 'name=test' \
    --data 'url=http://mockbin.com/requests'

Create a route for the test service, capturing a user_id field from the third segment of the request path:

Kubernetes users: Version v1beta1 of the Ingress specification does not allow the use of named regex capture groups in paths. If you use the ingress controller, you should use unnamed groups, e.g. (\w+)/instead of (?&lt;user_id&gt;\w+). You can access these based on their order in the URL path. For example $(uri_captures[1]) obtains the value of the first capture group.

curl -X POST http://localhost:8001/services/test/routes --data "name=test_user" \
    --data-urlencode 'paths=~/requests/user/(?<user_id>\w+)'

Enable the request-transformer-advanced plugin to add a new header, x-user-id, whose value is being set from the captured group in the route path specified above:

curl -XPOST http://localhost:8001/routes/test_user/plugins --data "name=request-transformer-advanced" --data "config.add.headers=x-user-id:\$(uri_captures['user_id'])"

Now send a request with a user id in the route path:

curl -i -X GET localhost:8000/requests/user/foo

You should notice in the response that the x-user-id header has been added with a value of foo.

Order of Execution

This plugin performs the response transformation in the following order:

  • remove → rename → replace → add → append

Configuration Examples

Add multiple headers by passing each header:value pair separately:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers[1]=h1:v1" \
  --data "config.add.headers[2]=h2:v1"
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

Add multiple headers by passing comma separated header:value pair:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v1,h2:v2"
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

Add multiple headers passing config as a JSON body:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "request-transformer-advanced", "config": {"add": {"headers": ["h1:v2", "h2:v1"]}}}'
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

Add a query string and a header:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.querystring=q1:v2,q2=v1" \
  --data "config.add.headers=h1:v1"
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1
h3: v1 h1: v1, h2: v1, h3: v1
Incoming Request Query String Upstream Proxied Query String
?q1=v1 ?q1=v1&q2=v1
  ?q1=v2&q2=v1

Append multiple headers and remove a body parameter:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v2,h2:v1" \
  --data "config.remove.body=p1" \
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h1: v2, h2: v1
Incoming URL Encoded Body Upstream Proxied URL Encoded Body
p1=v1&p2=v1 p2=v1
p2=v1 p2=v1

Add multiple headers and query string parameters if not already set:

curl -X POST http://localhost:8001/services/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v1,h2:v1" \
  --data "config.add.querystring=q1:v2,q2:v1" \
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1
h3: v1 h1: v1, h2: v1, h3: v1
Incoming Request Query String Upstream Proxied Query String
?q1=v1 ?q1=v1&q2=v1
  ?q1=v2&q2=v1

Changelog

Kong Gateway 3.1.x

  • Added support for navigating nested JSON objects and arrays when transforming a JSON payload.

Kong Gateway 3.0.x

  • Removed the deprecated whitelist parameter. It is no longer supported.

Kong Gateway 2.1.x

  • Use allow instead of whitelist.