Securing your Flask application using Kratos and Keto

Nowadays the engineering community has many products for authentication in their frameworks. Lots of them have built-in features for authentication and a lot of libraries available for social sign-in. We have the Django framework, Flask, and python-social-auth to build almost everything we need to authenticate users in the pythonic world.

In this article, I'll show you an example of how to add everything we need for the user's authentication without writing lots of lines of code. The code used in this blog post is available on GitHub. We'll use Flask, flask cookie-cutter, docker, docker-compose, Postgres, Ory Kratos and Ory Keto.

Let's take a look at the login flow of our application using Ory Kratos and Ory Keto

What we will use in our project

Flask cookiecutter is a great tool to bootstrap our project structure. It's always a great idea to have ready-to-use linters, Dockerfile, and package management tools out of the box.
Postgres as an RDBMS. We will have two Postgres services running in two containers in this example. I think that it's a great idea to keep it simple without using custom scripts to have multiple databases available in a single docker-compose service.
Ory Kratos with UI to authenticate users.
Ory Keto as an access control service.

Setting up Ory Kratos

Ory Kratos will be responsible for storing identity data such as email/login and password. Using the quickstart guide we need to copy the contents of contrib/quickstart/kratos/email-password to the root of your project and then add the following content to the docker-compose:

// ...
  postgres-kratos:
    image: postgres:9.6
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_USER=kratos
      - POSTGRES_PASSWORD=secret
      - POSTGRES_DB=kratos
    networks:
      - intranet

  kratos-migrate:
    image: oryd/kratos:v0.8.0-alpha.3
    links:
      - postgres-kratos:postgres-kratos
    environment:
      - DSN=postgres://kratos:secret@postgres-kratos:5432/kratos?sslmode=disable&max_conns=20&max_idle_conns=4
    networks:
      - intranet
    volumes:
      - type: bind
        source: ./kratos
        target: /etc/config/kratos
    command: -c /etc/config/kratos/kratos.yml migrate sql -e --yes

  kratos:
    image: oryd/kratos:v0.8.0-alpha.3
    links:
      - postgres-kratos:postgres-kratos
    environment:
      - DSN=postgres://kratos:secret@postgres-kratos:5432/kratos?sslmode=disable&max_conns=20&max_idle_conns=4
    ports:
      - "4433:4433"

Setting up Ory Keto

You can get familiar with the concepts of Ory Keto reading the quickstart guide. These articles can give you a brief introduction to it. Since we need to manage access to the home page, we need to create a folder keto at the root of our project and have a keto/keto.yml file with the following content:

version: v0.7.0-alpha.1

log:
  level: debug

namespaces:
  - name: app
    id: 1

serve:
  read:
    host: 0.0.0.0
    port: 4466
  write:
    host: 0.0.0.0
    port: 4467

We need the following containers:

postgresd-auth is the database for Ory Keto.
keto-migrate that takes care of database migrations.
keto-perms is a wrapper to work with permissions using a command-line interface.
keto runs the server.

version: "3.7"

x-default-volumes: &default_volumes
  volumes:
    - ./:/app
    - node-modules:/app/node_modules
    - ./dev.db:/tmp/dev.db

services:
  oathkeeper:
    image: oryd/oathkeeper:v0.38
    depends_on:
      - kratos
    ports:
      - 8080:4455
      - 4456:4456
    command: serve proxy -c "/etc/config/oathkeeper/oathkeeper.yml"
    environment:
      - LOG_LEVEL=debug
    restart: on-failure
    networks:
      - intranet
    volumes:
      - ./oathkeeper:/etc/config/oathkeeper

  flask:
    build:
      context: .
    image: "kratos_app_example-development"
    environment:
      - FLASK_APP=autoapp.py
      - FLASK_ENV=development
    networks:
      - intranet
    restart: on-failure
    volumes:
      - type: bind
         
         

  
     
    
       
    
       
       
       
    
       

  
     
    
       
    
       
    
       
    
        
         
         
          

  
     
    
       
    
       
    
       
       
    
        
         
         
    
       
         

  
     
    
       
       
    
       
    
       
     

  
     
    
       
       
    
       

  
     
    
       
    
       
       
       
    
       

  
     
    
        
         
         
    
       
       
     [, , ]

Working with policies

Ory Keto has configured a namespace app to use in the Flask application. Following the guide Check whether a User has Access to Something I decided to implement a simple permission policy for the demo project:

Use the command line to manage permissions.
Use email for subjects without @ symbol.

Pros

Easy to use and maintain.
Can easily be automated using CI/CD pipelines.

Cons

Lack of UI can be dealbreaker for non-engineering staff
This permission policy can violate GDPR, HIPAA or any other compliances due to personal data usage.

Flask part

// ...
HTTP_STATUS_FORBIDDEN = 403


@blueprint.route("/", methods=["GET", "POST"])
def home():
    """Home page."""

    if 'ory_kratos_session' not in request.cookies:
        return redirect(settings.KRATOS_UI_URL)

    response = requests.get(
        f"{settings.KRATOS_EXTERNAL_API_URL}/sessions/whoami",
        cookies=request.cookies
    )
    active = response.json().get('active')
    if not active:
        abort(HTTP_STATUS_FORBIDDEN)

    email = response.json().get('identity', {}).get('traits', {}).get('email').replace('@', '')

    # Check permissions

    response = requests.get(
        f"{settings.KETO_API_READ_URL}/check",
        params={
            "namespace": "app",
            "object": "homepage",
            "relation": "read",
            "subject_id": email,
        }
    )
    if not response.json().get("allowed"):
        abort(HTTP_STATUS_FORBIDDEN)

    return render_template("public/home.html")

@blueprint.route("/oathkeeper", methods=["GET", "POST"])
def oathkeeper():
    """ An example route to demo oathkeeper integration with Kratos """
    return {"message": "greetings"}

You can find the full code used for this blog post on GitHub.

Nota bene

Consider having authorization and authentication packages that use the Ory Kratos SDK and the Ory Keto SDK. Instead of just calling magic endpoints, your code will be more readable when using an SDK.
Please pay attention to configure login session and cookies.
Skip the set up with the Ory Network.

Securing your Flask application using Kratos and Keto

What we will use in our project

Setting up Ory Kratos

Setting up Ory Keto

Working with policies

Flask part

Nota bene

Next steps

Further reading

How a redirect broke login with Apple for a full day

Ory OSS v25.4.0 launch recap: The future of secure Identity & Access Management

What we will use in our project

Setting up Ory Kratos

Setting up Ory Keto

Working with policies

Flask part

Nota bene

Next steps