# ADR-0006: Authentication and Authorization with Keycloak

## Status

Accepted

## Context

As part of our microservices architecture ([ADR-0003](0003-microservices-architecture.md)), we needed a robust and centralized solution for authentication and authorization. Key requirements included:

1. Single sign-on (SSO) across all services and applications
2. Support for multiple authentication methods (username/password, OAuth, SAML)
3. Fine-grained authorization with role-based access control (RBAC)
4. User management capabilities including self-registration and profile management
5. Integration with external identity providers
6. Security best practices including password policies and account lockout
7. Token-based authentication for service-to-service communication

Implementing these features from scratch would be time-consuming and error-prone, and would divert resources from our core business functionality.

## Decision

We decided to use Keycloak (version 23.0) as our identity and access management solution. Keycloak is an open-source identity and access management solution that provides:

1. **User Authentication**: Multiple authentication methods and flows
2. **User Federation**: Integration with LDAP, Active Directory, and other user stores
3. **Identity Brokering**: Integration with external identity providers (Google, Facebook, etc.)
4. **Single Sign-On**: Across all applications and services
5. **Fine-grained Authorization**: Role-based and attribute-based access control
6. **User Management**: Self-registration, profile management, password policies
7. **Token-based Authentication**: JWT tokens for service-to-service communication

Our implementation includes:
- Keycloak server deployed as a containerized service
- Integration with our API Gateway for token validation
- Client adapters for our services and applications
- Custom themes and email templates
- Role and group definitions aligned with our domain model

## Consequences

### Positive

- **Comprehensive solution**: Keycloak provides a complete identity and access management solution
- **Standards compliance**: Keycloak implements industry standards (OAuth 2.0, OpenID Connect, SAML)
- **Reduced development effort**: We don't need to implement authentication and authorization from scratch
- **Security**: Keycloak follows security best practices and is actively maintained
- **Flexibility**: Keycloak supports multiple authentication methods and identity providers

### Negative

- **Operational complexity**: Keycloak adds another service to deploy and maintain
- **Learning curve**: Teams need to learn Keycloak concepts and APIs
- **Performance considerations**: Token validation adds some overhead to requests
- **Dependency**: We are dependent on Keycloak for authentication and authorization

### Neutral

- **Configuration needs**: Keycloak requires careful configuration to align with our security requirements
- **Upgrade management**: Keycloak upgrades need to be managed carefully

## Alternatives Considered

### Custom Authentication Service

We considered building our own authentication service. This would have given us complete control over the implementation but would have required significant development effort and ongoing maintenance.

### Auth0

We considered using Auth0, a commercial identity as a service (IDaaS) solution. Auth0 would have provided similar capabilities to Keycloak with less operational overhead, but would have introduced ongoing costs and potential vendor lock-in.

### Spring Security with JWT

We considered using Spring Security with JWT tokens for authentication and authorization. This would have integrated well with our Spring-based services but would have required more development effort and would not have provided the comprehensive identity management features of Keycloak.

## References

- [Keycloak Documentation](https://www.keycloak.org/documentation)
- [OAuth 2.0 and OpenID Connect](https://oauth.net/2/)
- [JWT (JSON Web Tokens)](https://jwt.io/)
- [Securing Microservices with Keycloak](https://www.keycloak.org/docs/latest/securing_apps/)