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Client credentials grant workflow
The client credentials grant is very similar to the password grant. The most important difference in the Kong OpenID Connect plugin is that the plugin itself does not try to authenticate. It just forwards the credentials passed by the client to the identity server’s token endpoint. The client credentials grant is visualized below:
sequenceDiagram autonumber participant client as Client
(e.g. mobile app) participant kong as API Gateway
(Kong) participant idp as IDP
(e.g. Keycloak) participant httpbin as Upstream
(backend service,
e.g. httpbin) activate client activate kong client->>kong: service with
basic authentication deactivate client kong->>kong: load basic
authentication credentials activate idp kong->>idp: keycloak/token
with client credentials deactivate kong idp->>idp: authenticate client activate kong idp->>kong: return tokens deactivate idp kong->>kong: verify tokens activate httpbin kong->>httpbin: request with access token httpbin->>kong: response deactivate httpbin activate client kong->>client: response deactivate kong deactivate client
Prerequisites
In most cases, the OpenID Connect plugin relies on a third party identity provider (IdP). The examples in this guide use Keycloak as a sample IdP.
Expand the following sections to configure Keycloak and Kong Gateway.
Configure Keycloak
All the *.test
domains in the following examples point to the localhost
(127.0.0.1
and/or ::1
).
We use Keycloak as the identity provider in the following examples, but the steps will be similar in other standard identity providers. If you encounter difficulties during this phase, refer to the Keycloak documentation.
- Create a confidential client
kong
withprivate_key_jwt
authentication and configure Keycloak to download the public keys from [the OpenID Connect Plugin JWKS endpoint][json-web-key-set]:
-
Create another confidential client
service
withclient_secret_basic
authentication. For this client, Keycloak will auto-generate a secret similar to the following:cf4c655a-0622-4ce6-a0de-d3353ef0b714
. Enable the client credentials grant for the client:
-
(Optional) Create another confidential client
cert-bound
with settings similar to theservice
client created previously. From the Advanced tab, enable the OAuth 2.0 Mutual TLS Certificate Bound Access Tokens Enabled toggle. -
(Optional, to test mTLS Client Authentication) Create another confidential client
client-tls-auth
with settings similar to theservice
client created above. From the Credentials tab, select the X509 Certificate Client Authenticator and fill the Subject DN field so that it matches the Kong client certificate’s, e.g.:CN=JohnDoe, OU=IT
. -
(Optional, to test Demonstrating Proof-of-Possession Client Authentication) Create another confidential client
client-dpop-auth
with settings similar to theservice
client created above. From the Advanced tab, enable theOAuth 2.0 DPoP Bound Access Tokens Enabled toggle. - Create a verified user with the name:
john
and the non-temporary password:doe
that can be used with the password grant:
Alternatively you can download the exported Keycloak configuration, and use it to configure the Keycloak. Please refer to Keycloak import documentation for more information.
You need to modify Keycloak standalone.xml
configuration file, and change the socket binding from:
<socket-binding name="https" port="${jboss.https.port:8443}"/>
to
<socket-binding name="https" port="${jboss.https.port:8440}"/>
The Keycloak default https
port conflicts with the default Kong TLS proxy port,
and that can be a problem if both are started on the same host.
Note: The mTLS Client Authentication, along with the proof of possession feature that validates OAuth 2.0 Mutual TLS Certificate Bound Access Tokens, both require configuring Keycloak to validate client certificates with mTLS using the
--https-client-auth=request
option, and to configure TLS appropriately, including adding the trusted client certificates to the truststore. For more information, refer to the Keycloak documentation.
Configure Kong Gateway
-
Create a service:
curl -i -X POST http://localhost:8001/services \ --data "name=openid-connect" \ --data "url=https://httpbin.konghq.com/anything"
-
Create a route:
curl -i -X POST http://localhost:8001/services/openid-connect/routes \ --data "name=openid-connect" \ --data "paths[]=/"
Set up the client credential grant
The following examples are built with simplicity in mind, and are not meant for a production environment. Because
httpbin.konghq.com
is the upstream service in these examples, we highly recommended that you do not run these examples with a production identity provider as there is a high chance of leaking information. The examples also use the plain HTTP protocol, which you should never use in production.
Using the Keycloak and Kong Gateway configuration from the prerequisites, set up an instance of the OpenID Connect plugin with the client credentials grant.
For the demo, we’re going to set up the following:
- Issuer, client ID, and client auth: settings that connect the plugin to your IdP (in this case, the sample Keycloak app).
- Auth method: client credentials grant.
- We want to search credentials for client credentials from the headers only.
With all of the above in mind, let’s test out the client credentials grant with Keycloak.
Enable the OpenID Connect plugin on the openid-connect
service:
Test the client credentials grant
At this point you have created a service, routed traffic to the service, and enabled the OpenID Connect plugin on the service. You can now test the client credentials grant.
-
Check the discovery cache:
curl -i -X GET http://localhost:8001/openid-connect/issuers
It should contain Keycloak OpenID Connect discovery document and the keys.
-
Request the service using the client credentials created in the Keycloak configuration step:
curl http://localhost:8000/openid-connect --user service:cf4c655a-0622-4ce6-a0de-d3353ef0b714
If you make another request using the same credentials, you should see that Kong adds less latency to the request as it has cached the token endpoint call to Keycloak.