Configure Buckit for Authentication using OpenID

Overview

Buckit supports using an OpenID Connect (OIDC) compatible IDentity Provider (IDP) such as Okta, KeyCloak, Dex, Google, or Facebook for external management of user identities.

This procedure covers:

Configuring a Buckit cluster for an external OIDC provider.
Using the Buckit AssumeRoleWithWebIdentity Security Token Service (STS) API to generate temporary credentials for use by applications.

This procedure is generic for OIDC compatible providers. Defer to the documentation for the OIDC provider of your choice for specific instructions or procedures on authentication and JWT retrieval.

Prerequisites

OpenID-Connect (OIDC) Compatible IDentity Provider

This procedure assumes an existing OIDC provider such as Okta, KeyCloak, Dex, Google, or Facebook. Instructions on configuring these services are out of scope for this procedure.

The Buckit cluster must have bidirectional access to the OIDC provider.

Review Access Management Behavior

Ensure each user identity intended for use with Buckit has the appropriate claim configured such that Buckit can associate a policy to the authenticated user. An OpenID user with no assigned policy has no permission to access any action or resource on the Buckit cluster.

For JWT claim-based authentication, Buckit only supports OIDC flows using the OpenID Authorization Code Flow.

Access to Buckit Cluster

This procedure uses bm for performing operations on the Buckit cluster. Install bm on a machine with network access to the cluster. See Install the Buckit Manager for instructions on downloading and installing bm. This procedure assumes a configured alias for the Buckit cluster.

Configure Buckit with OpenID External Identity Management

Create a new OpenID Configuration

Use the bm idp openid add command to create a new OIDC configuration for the Buckit cluster. The following example command assumes using the JWT claims returned by the OIDC provider for authorization through policy assignment.
```
bm idp openid add ALIAS \
  client_id=buckit-oidc-client-id \
  client_secret=buckit-oidc-client-secret \
  config_url="https://openid-provider.example.net/REALM/.well-known/openid-configuration" \
  claim_name="buckit-policies" \
  scopes="openid,groups"
```
You can also configure RoleArn-based functionality where all authenticated users have a single policy dictated by the role_policy setting. For example, set role_policy="readOnly" to assign all authenicated users the built-in read-only policy.
Review the Buckit Server logs

The Buckit process restarts as part of the new configuration. Examine the logs to ensure the OIDC configuration persisted successfully.

If configuring role_policy for one or more configurations, the output includes an ARN for use with the STS API.
Generate S3-Compatible Temporary Credentials using OIDC Credentials

Buckit requires clients authenticate using AWS Signature Version 4 protocol with support for the deprecated Signature Version 2 protocol. Specifically, clients must present a valid access key and secret key to access any S3 or Buckit administrative API, such as PUT, GET, and DELETE operations.

Applications can generate temporary access credentials as-needed using the AssumeRoleWithWebIdentity Security Token Service (STS) API endpoint and the JSON Web Token (JWT) returned by the OIDC provider.

The application must provide a workflow for logging into the OIDC provider and retrieving the JSON Web Token (JWT) associated to the authentication session. Defer to the provider documentation for obtaining and parsing the JWT token after successful authentication. Buckit provides an example Go application web-identity.go with an example of managing this workflow.

Once the application retrieves the JWT token, use the AssumeRoleWithWebIdentity endpoint to generate the temporary credentials:
```
POST https://buckit.example.net?Action=AssumeRoleWithWebIdentity
&WebIdentityToken=TOKEN
&Version=2011-06-15
&DurationSeconds=86400
&Policy=Policy
```
- Replace the TOKEN with the JWT token returned in the previous step.
- Replace the DurationSeconds with the duration in seconds until the temporary credentials expire. The example above specifies a period of 86400 seconds, or 24 hours.
- Replace the Policy with an inline URL-encoded JSON policy that further restricts the permissions associated to the temporary credentials.
  
  Omit to use the policy associated to the OpenID user policy claim.
You can optionally include the RoleArn parameter with the ARN string of your preferred single-policy OIDC configuration.

The API response consists of an XML document containing the access key, secret key, session token, and expiration date. Applications can use the access key and secret key to access and perform operations on Buckit.

See the AssumeRoleWithWebIdentity for reference documentation.