# Authx - Proof of Concept

This repository explores various authentication and authorization workflows by introducing a separate authn/authz service.
It serves as a proof of concept to illustrate potential workflows, not a production ready implementation.

To keep the implementation accessible, external dependencies have been minimized, ensuring a clear reference for understanding key concepts, including:

* SAML based authentication including IdP chaining to external identity providers
* OIDC based authentication
* OAuth endpoints with links to relevant RFCs for proper usage guidance

Below is a recording of a SAML based service provider initiated login, displaying raw SAML XML to illustrate each step of the workflow.

![SAML Login](./screencast.webm)

## Experiments

### Twirp + gRPC (AuthZ)

This experiment exposes a gRPC endpoint that aligns with the [`Ability.allowed?(subject, permission, resource)`][1] interface from GitLab's declarative authorization logic.

It demonstrates a headless authorization service that provides a low-latency decision point for other services to verify permissions.

Actors in this experiment:

* Headless authz service: A facade over GitLab’s existing declarative policies.
* API (Resource Server in OAuth terms): A slimmed-down GitLab REST API that delegates authorization decisions to the authz service.

### SAML, OIDC, OAuth

This experiment showcases how a separate authx service can handle both authentication and authorization using standard protocols:

* SAML & OIDC for authentication
* OAuth for authorization

Actors in this experiment:

* Authx service: Acts as a SAML Identity Provider and an OAuth Authorization Server.
* API: A slimmed-down GitLab REST API.

### API Gateway

This experiment explores a stateless authorization mechanism by integrating a policy DSL (such as [Casbin][3]) into a reverse proxy.
Authorization decisions are made early in the request pipeline based on HTTP request headers and body content.

### Sidecar Process

This experiment demonstrates a sidecar approach for making authorization decisions within an nginx process.
Inspired by [Open Policy Agent][4] deployments. This experiment:

* Uses lua bindings in nginx to connect to a local client process.
* The client process proxies requests to a gRPC based policy decision service.

## Questions

1. What is the unique identifier for each security principal across service boundaries? (i.e. bigint, ulid, uuid, email)

[1]: https://gitlab.com/gitlab-org/gitlab/-/blob/e1f6db024561e35462ac8d9f54b8f9678f6ed6ee/app/models/ability.rb#L73
[2]: https://gitlab.com/gitlab-org/gitlab/-/tree/master/app/policies
[3]: https://casbin.org/
[4]: https://www.openpolicyagent.org/