ContainerImage.Pinniped/site/content/docs/architecture.md

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Pinniped Architecture	layout docs

Architecture

The principal purpose of Pinniped is to allow users to access Kubernetes clusters. Pinniped hopes to enable this access across a wide range of Kubernetes environments with zero configuration.

Pinniped is composed of two parts.

1. The Pinniped Supervisor is an OIDC server which allows users to authenticate with an external identity provider (IDP), and then issues its own federation ID tokens to be passed on to clusters based on the user information from the IDP.
2. The Pinniped Concierge is a credential exchange API which takes as input a credential from an identity source (e.g., Pinniped Supervisor, proprietary IDP), authenticates the user via that credential, and returns another credential which is understood by the host Kubernetes cluster.

Pinniped supports various IDP types and implements different integration strategies for various Kubernetes distributions to make authentication possible.

Supported Kubernetes Cluster Types

Pinniped supports the following types of Kubernetes clusters:

• Clusters where the Kube Controller Manager pod is accessible from Pinniped's pods.

Support for other types of Kubernetes distributions is coming soon.

External Identity Provider Integrations

The Pinniped Supervisor will federate identity from one or more IDPs. Administrators will configure the Pinniped Supervisor to use IDPs via Kubernetes custom resources allowing Pinniped to be managed using GitOps and standard Kubernetes tools.

Pinniped supports the following IDPs.

1. Any OIDC-compliant identity provider (e.g., Dex, Okta).

The idp.supervisor.pinniped.dev API group contains the Kubernetes custom resources that configure the Pinniped Supervisor's upstream IDPs.

More IDP integrations are coming soon.

Authenticators

The Pinniped Concierge requires one or more authenticators to validate external credentials in order to issue cluster specific credentials. Administrators will configure authenticators via Kubernetes custom resources allowing Pinniped to be managed using GitOps and standard Kubernetes tools.

Pinniped supports the following authenticator types.

1. Any webhook which implements the Kubernetes TokenReview API.

   In addition to allowing the integration of any existing IDP which implements this API, webhooks also serve as an extension point for Pinniped by allowing for integration of arbitrary custom authenticators. While a custom implementation may be in any language or framework, this project provides a sample implementation in Golang. See the ServeHTTP method of cmd/local-user-authenticator/main.go.

2. A JSON Web Token (JWT) authenticator, which will validate and parse claims from JWTs. This can be used to validate tokens that are issued by the Pinniped Supervisor, any OIDC-compliant identity provider, or various other identity sources. The JWT authenticator provides the same functionality as the Kubernetes OIDC authentication mechanism, but it is configurable at cluster runtime instead of requiring flags to be set on the kube-apiserver process.

The authentication.concierge.pinniped.dev API group contains the Kubernetes custom resources that configure the Pinniped Concierge's authenticators.

Cluster Integration Strategies

Pinniped will issue a cluster credential by leveraging cluster-specific functionality. In the longer term, Pinniped hopes to contribute and leverage upstream Kubernetes extension points that cleanly enable this integration.

Pinniped supports the following cluster integration strategies.

• Pinniped hosts a credential exchange API endpoint via a Kubernetes aggregated API server. This API returns a new cluster-specific credential using the cluster's signing keypair to issue short-lived cluster certificates. (In the future, when the Kubernetes CSR API provides a way to issue short-lived certificates, then the Pinniped credential exchange API will use that instead of using the cluster's signing keypair.)

More cluster integration strategies are coming soon, which will allow Pinniped to support more Kubernetes cluster types.

kubectl Integration

With any of the above IDPs, authentication methods, and cluster integration strategies, kubectl commands receive the cluster-specific credential via a Kubernetes client-go credential plugin. Users may use the Pinniped CLI as the credential plugin, or they may use any proprietary CLI built with the Pinniped Go client library.

Example Cluster Authentication Sequence Diagrams

Concierge With Webhook

This diagram demonstrates using kubectl get pods with a Kubernetes client-go credential plugin that obtains an external credential to be sent to a webhook authenticator via the Pinniped Concierge.

Concierge with Supervisor

This diagram demonstrates using kubectl get pods with the Pinniped CLI functioning as a Kubernetes client-go credential plugin that obtains a federation ID token from the Pinniped Supervisor to be sent to a JWT authenticator via the Pinniped Concierge.