Add fine-grained authorization to a Rails app

Build a Rails controller for a blogging platform that registers users in Permit.io and allows only users with the Author role to create posts. This tutorial is for Ruby on Rails developers who want to enforce Permit.io policies from controller actions.

When you finish, your Rails app has two endpoints:

Endpoint	What it does
POST /register	Syncs a user to Permit.io and assigns the user the Reader role in the default tenant
POST /posts	Calls PERMIT.check() and returns 403 unless the user in the request has permission to create a Post

Prerequisites

• A Permit.io account. See Create a Permit.io account.
• Ruby and a Rails app created without the --api flag. The controller in this tutorial skips the verify_authenticity_token callback, which API-only Rails apps don't define.
• Node.js and npm, to install the Permit CLI.
• Docker, to run the policy decision point (PDP) container.

1. Configure the policy in Permit

Create the blogging platform policy with the Permit CLI. If your environment already has a policy with a Post resource and an Author role that can create posts, skip to 2. Get your API key.

1

Install the Permit CLI

The Permit CLI creates policies and runs the PDP from your terminal. Install the CLI with npm:

npm install -g @permitio/cli

Run permit to confirm that the CLI is installed.

2

Sign in with the Permit CLI

Authenticate the CLI with your Permit.io account:

permit login

The command opens a browser window where you sign in. After you sign in, the CLI uses your default environment. To use a different environment, run permit env select and choose the environment.

3

Apply the blogging platform template

Permit CLI templates create a policy with predefined resources, roles, and rules. To see the available templates, run permit env template list. The template source files are in the Permit CLI repository.

Apply the blogging-platform template to your environment:

permit env template apply --template blogging-platform

The CLI prints a success message when the template is applied.

4

Review the policy in the Policy Editor

In the Permit dashboard, select your project and open the Policy screen.

The blogging-platform template creates:

Policy element	What the template defines
Resources	Post (with a premium boolean attribute) and Comment, each with create, read, update, and delete actions
Roles	Admin (all actions), Author (create and read posts, read comments), Reader (create and read comments), and Premium Reader (read posts and comments)
Relationship	A Post is the parent of its Comment instances. An Author of a post instance becomes a Moderator of the comments on that post. This rule is relationship-based access control (ReBAC).
Resource set	Free Post contains posts where premium is false. Readers can read free posts. This rule is attribute-based access control (ABAC).

This tutorial uses one rule from the policy: the Author role can create a Post, and the Reader role cannot. To change which role can perform an action, check or clear the box in the Policy Editor.

2. Get your API key

Your Rails app and the PDP authenticate with Permit.io with your environment API key. Copy the API key of the environment where you applied the template. See Get your API key.

Keep the API key out of your code

Anyone with the environment API key can change that environment's policy through the Permit API. Load the key from an environment variable, and don't commit it.

3. Run the PDP

The PDP evaluates each permission check against your policy. Start a PDP container with the Permit CLI:

permit pdp run

The command starts the PDP in Docker and prints the container ID and name. The PDP listens on port 7766, so your app connects to it at http://localhost:7766.

The Free Post resource set is an ABAC rule, and the Cloud PDP doesn't evaluate ABAC rules, so run the container PDP for this policy. To run the container with docker run instead, or to check that the PDP is healthy, see Run the PDP.

4. Build the Rails app

1

Install the Ruby SDK

Add the Permit Ruby SDK to your Gemfile:

gem 'permit-sdk'

Install the gem:

bundle install

For the SDK reference, see Check permissions with the Ruby SDK.

2

Initialize the Permit client

Create config/initializers/permit.rb with the following code:

# config/initializers/permit.rb
require 'permit'

raise "PERMIT_API_KEY is not set" unless ENV['PERMIT_API_KEY']
raise "PDP_URL is not set" unless ENV['PDP_URL']

PERMIT = Permit.new(
  ENV['PERMIT_API_KEY'],
  ENV['PDP_URL']
)

Rails runs the initializer at startup and stores the client in the PERMIT constant. The initializer raises an error, and the app doesn't start, when either environment variable is missing:

Variable	Value
PERMIT_API_KEY	Your environment API key from 2. Get your API key
PDP_URL	The PDP address from 3. Run the PDP: http://localhost:7766

3

Create the Permit controller

Create app/controllers/permit_controller.rb with the following code:

# app/controllers/permit_controller.rb
require 'net/http'

class PermitController < ApplicationController
  skip_before_action :verify_authenticity_token

  def register
    user = PERMIT.api.users.sync_user(
      key: params[:email],
      email: params[:email],
      first_name: params[:first_name],
      last_name: params[:last_name]
    )
    assigned_role = {
      user: params[:email],
      role: 'Reader',
      tenant: 'default'
    }
    response = assign_role(assigned_role)
    render json: {
      message: 'User registered and role assigned',
      user: user,
      role_assignment: response
    }, status: :created
  rescue => e
    render json: { error: e.message }, status: :internal_server_error
  end

  def posts
    permitted = PERMIT.check(
      params[:user],
      'create',
      'Post'
    )
    if permitted
      render json: { message: "User is permitted" }
    else
      render json: { message: "User is not permitted" }, status: :forbidden
    end
  rescue => e
    render json: { error: e.message }, status: :internal_server_error
  end

  private

  # The Ruby SDK has no role assignment method, so call the Permit REST API
  def assign_role(assignment)
    api = URI('https://api.permit.io')
    headers = { 'Authorization' => "Bearer #{ENV['PERMIT_API_KEY']}", 'Content-Type' => 'application/json' }
    Net::HTTP.start(api.host, api.port, use_ssl: true) do |http|
      scope = JSON.parse(http.get('/v2/api-key/scope', headers).body)
      path = "/v2/facts/#{scope['project_id']}/#{scope['environment_id']}/role_assignments"
      JSON.parse(http.post(path, assignment.to_json, headers).body)
    end
  end
end

The controller has two actions:

Action	What it does
register	Syncs the user to Permit.io with the email address as the user key, then assigns the Reader role in the default tenant with the assign_role helper, which calls the Permit REST API because the Ruby SDK has no role assignment method. Returns 201 with the user and the role assignment.
posts	Asks the PDP whether the user key in params[:user] can create a Post. Returns "User is permitted", or 403 with "User is not permitted".

Both actions return 500 with the error message when a call to Permit.io or the PDP raises an error.

note

In a production app, take the user key from your authenticated session. This example reads the user key from the request parameters so that you can test the endpoint with curl.

4

Add the routes

Map the two endpoints to the controller actions in config/routes.rb:

# config/routes.rb
Rails.application.routes.draw do
  post '/register', to: 'permit#register'
  post '/posts', to: 'permit#posts'
end

5

Start the Rails app

Set the environment variables and start the server, replacing <YOUR_API_KEY> with your API key:

export PERMIT_API_KEY=<YOUR_API_KEY>
export PDP_URL=http://localhost:7766
bin/rails server

The app listens on http://localhost:3000.

5. Test the permission check

Register two users, give one of them the Author role, and confirm that the PDP allows only that user to create a post.

1

Register two users

In a second terminal, register John and Emma:

curl -X POST http://localhost:3000/register \
  -H "Content-Type: application/json" \
  -d '{"email": "john@example.com", "first_name": "John", "last_name": "Doe"}'

curl -X POST http://localhost:3000/register \
  -H "Content-Type: application/json" \
  -d '{"email": "emma@example.com", "first_name": "Emma", "last_name": "Den"}'

Each request returns HTTP 201 with "message": "User registered and role assigned", the synced user under user, and the Reader role assignment under role_assignment.

2

Assign John the Author role

Both users have the Reader role, which can't create posts. Give John the Author role in the Permit dashboard:

1. Open the Directory screen and select john@example.com to open the Edit User panel.
2. Under Permissions Per Tenant, select the Default Tenant.
3. In Top Level Access, add the Author role.
4. Click Save.

For other ways to assign roles, including the API and SDK, see Sync users.

3

Check that John can create a post and Emma can't

Send a POST /posts request for John:

curl -X POST http://localhost:3000/posts \
  -H "Content-Type: application/json" \
  -d '{"user": "john@example.com"}'

The PDP allows the request because John has the Author role. The app returns {"message":"User is permitted"}.

Send the same request for Emma:

curl -X POST http://localhost:3000/posts \
  -H "Content-Type: application/json" \
  -d '{"user": "emma@example.com"}'

The PDP denies the request because Emma has only the Reader role. The app returns HTTP 403 with {"message":"User is not permitted"}.

Each check also appears in the Audit Log screen of the Permit dashboard, with the user, action, resource, and decision.

Next steps

• Check permissions with the Ruby SDK: SDK installation and more permit.check() examples.
• Check permissions with permit.check(): check against tenants, resource instances, and attributes.
• Build RBAC policies: create roles and permissions for your own resources.
• Connect your authentication provider: use the identity from your sign-in flow as the Permit.io user key.

Next step

Going to production? Review the PDP deployment checklist, or talk to an engineer about scale and latency.