feat(03-AgentCore-identity): Add private Keycloak IdP samples with VPC Lattice

[CameronKeeneAWS]

Amazon Bedrock AgentCore Samples Pull Request

[!IMPORTANT]

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Issue number: #1447

Concise description of the PR

• Adds two end-to-end samples demonstrating how to connect Amazon Bedrock AgentCore Identity to a privately hosted Keycloak IdP using Amazon VPC Lattice privateEndpoint, because many enterprises run Keycloak or similar OIDC providers in private networks with no public internet exposure and need a secure connectivity pattern for JWT validation.

User experience
Before: No sample existed showing how to integrate AgentCore with a private (non-internet-facing) Keycloak identity provider. Users wanting to use private IdPs with AgentCore received "Invalid inbound token" errors with no reference architecture to resolve the issue.

After: Users can follow fully automated deployments (deploy_sample.sh / cleanup_sample.sh) that provision:

• A Keycloak 26 instance on EC2 behind an internal ALB with ACM certificate
• VPC Lattice connectivity (AgentCore-managed mode)
• Sample 13: AgentCore Runtime with CUSTOM_JWT auth validated against the private IdP
• Sample 14: AgentCore Gateway with Lambda-backed MCP tools authenticated via the private IdP

The samples include architecture diagrams, CloudFormation templates, Keycloak setup scripts, and complete teardown scripts.

Checklist

• I have reviewed the contributing guidelines
• Add your name to CONTRIBUTORS.md
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Are you uploading a dataset?
• Have you documented Introduction, Architecture Diagram, Prerequisites, Usage, Sample Prompts, and Clean Up steps in your example README?
• I agree to resolve any issues created for this example in the future.
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Acknowledgment
By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.