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TLS Handshake Modifier

The plugin requests, but does not require the client certificate. No validation of the client certificate is performed. If a client certificate exists, the plugin makes the certificate available to other plugins acting on this request.

This plugin must be used in conjunction with the TLS Metadata Headers plugin.

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 tls-handshake-modifier plugin on a service.

Make the following request:

curl -X POST http://localhost:8001/services/SERVICE_NAME|SERVICE_ID/plugins \
    --data "name=tls-handshake-modifier"

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: tls-handshake-modifier-example
config:
  EXAMPLE_PARAMETER: EXAMPLE_VALUE
plugin: tls-handshake-modifier

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: tls-handshake-modifier-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: tls-handshake-modifier
  service: SERVICE_NAME|SERVICE_ID
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

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 Konnect UI.

From the servicehub icon Service Hub, select a service version, then set up the plugin:

  1. In the Plugins section, click Add Plugin.
  2. Find and select the TLS Handshake Modifier plugin.
  3. Click Create.

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 TLS Handshake Modifier 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 tls-handshake-modifier plugin on a route.

Make the following request:

curl -X POST http://localhost:8001/routes/ROUTE_NAME|ROUTE_ID/plugins \
  --data "name=tls-handshake-modifier"

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: tls-handshake-modifier-example
config:
  EXAMPLE_PARAMETER: EXAMPLE_VALUE
plugin: tls-handshake-modifier

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: tls-handshake-modifier-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: tls-handshake-modifier
  route: ROUTE_NAME
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

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 Konnect UI.

From the servicehub icon Service Hub, select a service version, then set up the plugin:

  1. Select a route.
  2. In the Plugins section, click Add Plugin.
  3. Find and select the TLS Handshake Modifier plugin.
  4. Click Create.

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 TLS Handshake Modifier 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.

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 tls-handshake-modifier plugin globally.

Make the following request:

curl -X POST http://localhost:8001/plugins/ \
  --data "name=tls-handshake-modifier"

Create a KongClusterPlugin resource and label it as global:

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-tls-handshake-modifier>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config:
  <optional_parameter>: <value>
plugin: tls-handshake-modifier

Add a plugins entry in the declarative configuration file:

plugins:
- name: tls-handshake-modifier
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

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 TLS Handshake Modifier 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 tls-handshake-modifier.
service.name or service.id

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

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.
enabled

Type: boolean

Default value: true		 Whether this plugin will be applied.
config.tls_client_certificate
optional

Type: string

Default value: REQUEST

Indicates the TLS handshake preference. The only option is REQUEST, which requests the client certificate.

Client certificate request

Client certificates are requested in the ssl_certificate_by_lua phase where Kong Gateway does not have access to route and workspace information. Due to this information gap, Kong Gateway asks for the client certificate on every handshake if the tls-handshake-modifier plugin is configured on any route or service.

In most cases, the failure of the client to present a client certificate doesn’t affect subsequent proxying if that route or service does not have the tls-handshake-modifier plugin applied. The exception is where the client is a desktop browser, which prompts the end user to choose the client cert to send and leads to user experience issues rather than proxy behavior problems.

To improve this situation, Kong builds an in-memory map of SNIs from the configured Kong Gateway routes that should present a client certificate. To limit client certificate requests during a handshake while ensuring the client certificate is requested when needed, the in-memory map is dependent on all the routes in Kong Gateway having the SNIs attribute set. When no routes have SNIs set, Kong Gateway must request the client certificate during every TLS handshake:

  • On every request irrespective of workspace when the plugin is enabled in global workspace scope.
  • On every request irrespective of workspace when the plugin is applied at the service level and one or more of the routes do not have SNIs set.
  • On every request irrespective of workspace when the plugin is applied at the route level and one or more routes do not have SNIs set.
  • On specific requests only when the plugin is applied at the route level and all routes have SNIs set.

The result is all routes must have SNIs if you want to restrict the handshake request for client certificates to specific requests.