logan-connolly / python-sqlalchemy-cerbos

An example application of integrating Cerbos with a FastAPI server using SQLAlchemy as the ORM.

python-sqlalchemy-cerbos

An example application of integrating Cerbos with a FastAPI server using SQLAlchemy as the ORM. Cerbos helps you super-charge your authorization implementation by writing context-aware access control policies for your application resources. Author access rules using an intuitive YAML configuration language, use your Git-ops infrastructure to test and deploy them and, make simple API requests to the Cerbos PDP to evaluate the policies and make dynamic access decisions.

Dependencies

• Python >= 3.8
• SQLAlchemy >= 1.4 / 2.0
• Docker for running the Cerbos Policy Decision Point (PDP)

Getting Started

1. Start up the Cerbos PDP instance docker container. This will be called by the FastAPI app to check authorization.

cd cerbos
./start.sh

2. Install python dependencies

# from project root
pdm install

3. Start the FastAPI dev server

pdm run demo

Sample data

On startup, the app will create an in-memory SQLite instance, and populate it with some sample data - see here.

The following users will be created. Authentication is done via Basic authentication using the provided Usernames (password is omitted). The Role and Department is loaded from the database after successful authentication.

ID	Username	Role	Department
1	alice	Admin	IT
2	john	User	Sales
3	sarah	User	Sales
4	geri	User	Marketing

Policies

This example has a simple CRUD policy in place for a resource kind of contact - like a CRM system would have. The policy files can be found in the cerbos/policies folder here.

Should you wish to experiment with this policy, you can try it in the Cerbos Playground.

The policy expects one of two roles to be set on the principal - admin and user and an attribute which defines their department as either Sales or Marketing.

These roles are authorized as follows:

Action	Role: Admin	Derived Role: Owner (User)	Role: User, department: Sales	Role: User, department: Marketing
read	Y	Y	if Contact is active	if Contact is active and opted in to marketing
update	Y	Y
delete	Y	Y
create	Y		Y

Example Requests

Get all contacts

curl -i http://john@localhost:8000/contacts

Get a contact

As a Sales user => 200 OK

curl -i http://john@localhost:8000/contacts/2

As a Marketing user => 403 Unauthorized

curl -i http://geri@localhost:8000/contacts/2