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Build a Simple Policy

In this guide, you’ll learn about Authorization Policies in Pomerium.

Specifically, we’ll cover:

  • What an authorization policy is
  • Why you need policies to enforce access control
  • How Pomerium Policy Language (PPL) works
  • How to build your own policies to protect upstream apps and services
Before You Start

Make sure you’ve completed the following tutorials:

If you completed these tutorials, you should have:

  • A route pointing to Grafana
  • A route pointing to the Verify service

Each tutorial builds on the same configuration files. In this tutorial, you’ll build simple policies to secure your services.

What is an Authorization Policy?​

An Authorization Policy defines what resources a user (or group of users) can access within an organization. It’s the logic that tells Pomerium, “this HR employee isn’t authorized to access the engineering staging app.”

From a purely functional point of view, authorization policies seem like a simple concept: They help manages access to apps and services in your organization. But, they can get pretty complicated as your organization scales.

To help you ease into building policies with Pomerium, you should first learn how to build policies in Pomerium with Pomerium Policy Language (PPL).

After that, you’ll check out some PPL examples and write your own policies for your routes.

Let’s get started!

What is Pomerium Policy Language (PPL)?​

PPL is a YAML-based notation for creating easy and flexible authorization policies.

PPL allows administrators to express authorization policy in a high-level, declarative language that promotes safe, performant, fine-grained controls.

You can think of it as coded instructions to tell Pomerium how authorization decisions are made for capturing all niche and edge-case scenarios. It’s as flexible as you want it to be!

How does PPL work?​

PPL consists of Rules, Actions, Logical Operators, Criteria, and Matchers.

Rules​

A PPL document is either an object or an array of objects. The object represents a rule where the action is the key and the value is an object containing the logical operators.

Actions​

Only two actions are supported: allow and deny. deny takes precedence over allow. More precisely: a user will have access to a route if at least one allow rule matches and no deny rules match.

Logical Operators​

A logical operator combines multiple criteria together for the evaluation of a rule.

There are four logical operators:

  • and
  • or
  • not
  • nor

Criteria​

Criteria in PPL are represented as an object where the key is the name and optional sub-path of the criterion, and the value changes depending on which criterion is used.

Matchers​

Matchers can be used with logical operators like criteria. PPL offers a variety of matchers, like:

  • Certificate Matcher
  • Day of Week Matcher
  • Date Matcher
  • Device Matcher
  • String Matcher
  • Time of Day Matcher

For an in-depth look at how PPL works, see the Policy Language page.

Example policies with PPL​

Now that you’ve briefly covered PPL, let’s jump into some simple examples:

Example 1: Allow access if the user's email address exactly matches the criterion's value

This example instructs Pomerium to only grant a user access if their email address is example@domain.com.

PPL rule
policy: # Policy object starts here
  allow: # At least one action
    and: # Logical operator
      - email: # Criterion
        is: example@domain.com # Value

Example 2: Allow access based on the domain criterion

Requiring an exact email address is one way to secure an app, but it won't let anyone else in without that specific email address. This obviously won't scale for an organization where multiple members may require access to the same service.

Instead of specifying the entire email address, you can write a policy that allows access if a user has the required domain in their email address (the part after @).

The example below instructs Pomerium to only grant a user access if their email address matches the domain criterion’s value.

policy:
  allow:
    and:
      - domain:
          is: example.com

Again, the domain criterion checks for the domain portion of the user’s email address. Using the example above, if your email were bob@gmail.com, Pomerium would deny you access; if your email were bob@example.com, Pomerium would grant you access.

Example 3: Use logical operators to allow access based on username or domain criteria

The policy below uses the or operator, which allows access if either of two conditions is true. In this example, Pomerium will grant access if the email address domain is example.com or the username is user2.

If neither of these conditions is true, the policy will deny a user access.

policy:
  allow:
    or:
      - domain:
          is: example.com
      - user:
          is: user2
tip

The example above defines the user criterion as user2. In a real-world application, an identity provider may not reference the actual "username" value in a JWT; instead, it likely includes the user's unique ID, which is often the value of the subject or user claim (or both).

To ensure your policies are enforced correctly, use the unique ID instead of the actual username. For example, if the ID associated with user2 is 1234567890#$%^, the policy would look like this:

policy:
  allow:
    or:
      - domain:
          is: example.com
      - user:
          is: '1234567890#$%^'

Now that we’ve covered some examples, it’s time to attach a policy to a route.

Build policies for your routes​

By now, your configuration file should have routes for the Verify service and Grafana. You may have noticed that these routes have the allow_any_authenticated_user setting attached to them.

That’s a great setting to test a route with, but we want to secure these routes with policies now.

In your Pomerium configuration file:

  • Remove the allow_any_authenticated_user: true setting from your Grafana route
  • Remove the policy block attached to the Verify service
  • Add this policy block below each route (and update the example.com domain with your domain):
policy:
  allow:
    and:
      - domain:
        is: example.com

Now, access the route.

Pomerium will grant you access to either service if your email address contains the right domain.

Great job!

Summary​

Now that you’ve built a route and policy to control access, you have the basic building blocks in place to start using Pomerium.

To sum up what you have so far:

  • An instance of Pomerium with Docker
  • The know-how of how routes and policies work

These are the basics for a reverse proxy, which is intended to act as a public facing representative of the application or service. Everything after is security:

  • Who is coming in?
  • What are they allowed to do?
  • Should Pomerium let it happen?

We start with the first question by setting up Identity Verification.

Configuration file state​

By now, your configuration files should look similar to this:

authenticate_service_url: https://authenticate.pomerium.app

routes:
  - from: https://verify.localhost.pomerium.io
    to: http://verify:8000
    policy:
      allow:
        and:
          - domain:
              is: example.com
  - from: https://grafana.localhost.pomerium.io
    to: http://grafana:3000
    policy:
      allow:
        and:
          - domain:
              is: example.com

Docker Compose:

version: '3'
services:
  pomerium:
    image: cr.pomerium.com/pomerium/pomerium:latest
    volumes:
      - ./config.yaml:/pomerium/config.yaml:ro
    ports:
      - 443:443
  verify:
    image: cr.pomerium.com/pomerium/verify:latest
    expose:
      - 8000
  grafana:
    image: grafana/grafana:latest
    ports:
      - 3000:3000
    volumes:
      - grafana-storage:/var/lib/grafana
volumes:
  grafana-storage: