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Third-party OAuth2 Support for Application Registration

Third-party OAuth2 support allows developers to centralize application credentials management with the supported Identity Provider of their choice. To use the external IdP feature, set the portal_app_auth configuration option to external-oauth2 in the kong.conf.default configuration file. For more information, see setting the Authorization Provider Strategy.

The Kong OIDC and Portal Application Registration plugins are used in conjunction with each other on a Service:

The OIDC plugin handles all aspects of the OAuth2 handshake, including looking up the Consumer via custom claim (the custom_id matches the identity provider client_id claim).
The Application Registration plugin is responsible for checking the mapped Consumer and ensuring the Consumer has the correct ACL (Access Control List) permissions to access the Route.

Supported identity providers

The Kong OIDC plugin supports many identity providers out of the box. The following providers have been tested for the current version of the Kong Portal Application Registration plugin used in tandem with the Kong OIDC plugin:

Resources

How you authenticate with a Service depends on its underlying OAuth2 implementation. For more information, reference the documentation below for your implemented identity provider and OAuth flow.

Supported OAuth flows

Client Credentials (RFC 6742 Section 4.4)
Authorization Code (RFC 6742 Section 4.1)
Implicit Grant (RFC 6742 Section 4.2)
Password Grant (RFC 6742 Section 4.3)

Password Grant and Implicit Grant flows are available but not recommended because they are less secure than the Authorization Code and Client Credentials flows.

Client Credentials Flow

The OIDC plugin makes authenticating using Client Credentials very straightforward. This flow should be used for server-side and secure machine-to-machine communication. The Client Credentials flow requires the authorizing party to store and send the application’s client_secret.

In this flow, a developer makes a request against the Service with the OIDC and Application Registration plugins applied. This request should contain the client_id and client_secret as a Basic Auth authentication header:

Authorization: Basic client_id:client_secret

The client_id:client_secret should be base64-encoded.

The following sequence diagram illustrates the Client Credentials flow through the OIDC and Application Registration plugins. Click on the image to expand its view.

Client Credentials Flow

Step	Explanation
a	Developer sends the Okta application’s `client_id` and `client_secret` to the Route. The OIDC plugin proxies this request to the Okta auth server’s endpoint.
b	Okta reads the `client_id` and `client_secret` and generates an access token. The auth server is configured to insert a custom claim `application_id`, which is a key/value pair with the Okta application’s `client_id`.
c	Okta returns the access token to Kong.
d	The OIDC plugin reads the resulting access token and associates the request with the application via the `application_id` custom claim.
e	If the resolved application has permission to consume the Service via its Portal Application Registration plugin, Kong forwards the request to the Upstream.

Authorization Code Flow

Due to limitations of the OIDC plugin, a single plugin instance cannot handle dynamic client_id's provisioned from multiple sources (applications). To circumvent this issue, the IdP Issuer URL is exposed to developers on the Dev Portal application show page when show_issuer is enabled in the Application Registration plugin. Developers can hit the Issuer URL directly to provision an access token. After getting the access token, requests can be made against the proxy.

Set up the application to secure an access token against the IdP directly. For more information about implementing the Authorization Code flow with Okta, refer to the Okta developer guide.
After the initial access token handshake has been completed, make subsequent requests to the Kong service using that access token as a bearer token. After the first successful request, the OIDC plugin will establish a session with the client so that the access token does not need to be continually passed with every request.

The following sequence diagram illustrates the Authorization Code flow through the OIDC and Application Registration plugins. Click on the image to expand its view.

Authorization Code Flow

Step	Explanation
a	A developer copies the target Service’s `issuer_id`, which can be exposed in the Dev Portal application view Service Details page. Developers can configure their application to make a request to this endpoint to authenticate the user and retrieve an access token.
b	Okta redirects the user to a login page.
c	The user inputs their Single Sign-On (SSO) information.
d	The user submits the SSO form that contains their Okta username and password.
e	Upon a successful login, the application is given an access token to make against calls for all subsequent requests.
f	The user makes a request to the protected Service and Route.
g	The OIDC plugin takes the access token and runs introspection, consulting the Okta authorization server if necessary. After the access token has been verified, the plugin matches the custom claim to find the associated application Consumer via its `custom_id`.
h	The request is passed to the Application Registration plugin, which checks to make sure the Consumer has the appropriate ACL (Access Control List) permissions.
i	The request is proxied to the Upstream.

Implicit Grant Flow

The Implicit Grant flow is not recommended if the Authorization Code flow is possible.

Set up the application to secure an access token against the IdP directly. For more information about implementing the Implicit Grant flow with Okta, refer to the Okta developer guide.
After the access token handshake has been completed, make subsequent requests to the Kong service using that access token as a bearer token. After the first successful request, the OIDC plugin will establish a session with the client so that the access token does not need to be passed continuously.