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Keycloak on LocalStack

This repo contains a LocalStack Extension that runs Keycloak alongside LocalStack for identity and access management with local AWS applications.

This Extension:

  • Spins up a Keycloak instance on LocalStack startup.
  • Auto-registers Keycloak as an OIDC identity provider in LocalStack IAM.
  • Ships with a default realm (localstack) ready for OAuth2/OIDC flows.
  • Exchanges Keycloak JWTs for temporary AWS credentials via AssumeRoleWithWebIdentity.

Prerequisites

  • Docker
  • LocalStack Pro
  • localstack CLI
  • make

Installation

localstack extensions install "git+https://github.com/localstack/localstack-extensions.git#egg=localstack-keycloak&subdirectory=keycloak"

Install local development version

To install the extension into LocalStack in developer mode, you will need Python 3.11, and create a virtual environment in the extensions project.

make install

Then, to enable the extension for LocalStack, run

localstack extensions dev enable .

You can then start LocalStack with EXTENSION_DEV_MODE=1 to load all enabled extensions:

EXTENSION_DEV_MODE=1 localstack start

Usage

Start LocalStack:

localstack start

Keycloak will be available at:

Endpoint URL
Admin Console http://localhost:8080/admin
Token Endpoint http://keycloak.localhost.localstack.cloud:4566/realms/localstack/protocol/openid-connect/token
JWKS URL http://keycloak.localhost.localstack.cloud:4566/realms/localstack/protocol/openid-connect/certs

Keycloak ports are exposed directly on the host for easy access:

  • Admin Console & HTTP (8080): http://localhost:8080 - Use this for the admin UI and direct API access
  • Management (9000): http://localhost:9000 - Health and metrics endpoints (Keycloak 26+)

The gateway URL (keycloak.localhost.localstack.cloud:4566) is available for token endpoints and OIDC flows.

  • Default Admin Credentials: admin / admin
  • Health check: curl http://localhost:9000/health/ready

Get an Access Token

TOKEN=$(curl -s -X POST \
  "http://keycloak.localhost.localstack.cloud:4566/realms/localstack/protocol/openid-connect/token" \
  -d "grant_type=client_credentials" \
  -d "client_id=localstack-client" \
  -d "client_secret=localstack-client-secret" | jq -r '.access_token')

Exchange Token for AWS Credentials

# Create IAM role that trusts Keycloak
cat > trust-policy.json << 'EOF'
{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": {
      "Federated": "arn:aws:iam::000000000000:oidc-provider/keycloak.localhost.localstack.cloud:4566/realms/localstack"
    },
    "Action": "sts:AssumeRoleWithWebIdentity"
  }]
}
EOF

awslocal iam create-role \
  --role-name KeycloakAuthRole \
  --assume-role-policy-document file://trust-policy.json

# Exchange Keycloak token for AWS credentials
awslocal sts assume-role-with-web-identity \
  --role-arn arn:aws:iam::000000000000:role/KeycloakAuthRole \
  --role-session-name test-session \
  --web-identity-token "$TOKEN"

Configuration

Environment Variable Default Description
KEYCLOAK_REALM localstack Name of the default realm
KEYCLOAK_VERSION 26.0 Keycloak Docker image version
KEYCLOAK_REALM_FILE - Path to custom realm JSON file
KEYCLOAK_DEFAULT_USER - Username for auto-created test user
KEYCLOAK_DEFAULT_PASSWORD - Password for auto-created test user
KEYCLOAK_OIDC_AUDIENCE localstack-client Audience claim for OIDC provider
KEYCLOAK_FLAGS - Additional flags for Keycloak start command

Note: When using localstack start, prefix environment variables with LOCALSTACK_ (e.g., LOCALSTACK_KEYCLOAK_REALM).

Custom Realm Configuration

Use your own realm JSON file with pre-configured users, roles, and clients.

# The path must be an absolute HOST path for Docker mount
# Use LOCALSTACK_ prefix when running via CLI
LOCALSTACK_KEYCLOAK_REALM_FILE=/path/to/my-realm.json localstack start

See quickstart/sample-realm.json for a realm template and quickstart/README.md for a step-by-step guide.

Create Test Users

# Auto-create a test user on startup (use LOCALSTACK_ prefix with CLI)
LOCALSTACK_KEYCLOAK_DEFAULT_USER=testuser LOCALSTACK_KEYCLOAK_DEFAULT_PASSWORD=password123 localstack start

Default Client

The extension creates a default client localstack-client with:

  • Client Secret: localstack-client-secret
  • Flows: Authorization Code, Client Credentials, Direct Access Grants
  • Service Account Roles: admin, user

The service account for localstack-client is automatically assigned the admin realm role, enabling full access when using client credentials flow.

Sample Application

See the sample-app/ directory for a complete example demonstrating:

  • API Gateway with Lambda Authorizer
  • JWT validation with Keycloak
  • Role-based access control
  • DynamoDB user management

Troubleshooting

Keycloak takes a long time to start

Keycloak typically takes 30-60 seconds to fully start. The extension waits for the health check to pass before marking LocalStack as ready.

Health check endpoint returns 404

In Keycloak 26+, the health endpoint is on port 9000:

curl http://localhost:9000/health/ready

View Keycloak logs

docker logs ls-ext-keycloak

Development

# Install dependencies
make install

# Run tests (requires LocalStack with extension running)
make test

# Format code
make format

# Lint
make lint

License

Apache License 2.0