Add fine-grained authorization to a Gin app

Build a Gin API in Go 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 Go backend developers who want to enforce Permit.io policies from Gin routes and middleware.

When you finish, your Gin 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	Runs middleware that calls permitClient.Check() and returns 403 unless the user in the X-User header has permission to create a Post

Prerequisites

• A Permit.io account. See Create a Permit.io account.
• Go and a Go module for your app. The app uses Gin.
• 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 Gin 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 Gin app

All the Go code in this section goes in one file, main.go, in your Go module.

1

Install the Go SDK

In your Go module directory, install the Permit Go SDK:

go get github.com/permitio/permit-golang

The code in this tutorial also imports Gin (github.com/gin-gonic/gin), zap (go.uber.org/zap), and godotenv (github.com/joho/godotenv). After you add the code, run go mod tidy to download these modules. For all SDK options, see Check permissions with the Go SDK.

2

Declare the imports and the Permit client variable

Add the imports, a package-level permitClient variable, and the UserIn struct to main.go:

package main

import (
	"context"
	"log"
	"net/http"
	"os"

	"github.com/gin-gonic/gin"
	"github.com/joho/godotenv"
	"github.com/permitio/permit-golang/pkg/config"
	"github.com/permitio/permit-golang/pkg/enforcement"
	"github.com/permitio/permit-golang/pkg/models"
	"github.com/permitio/permit-golang/pkg/permit"
	"go.uber.org/zap"
)

var permitClient *permit.Client

// struct for user input
type UserIn struct {
	Email     string `json:"email" binding:"required,email"`
	FirstName string `json:"first_name" binding:"required"`
	LastName  string `json:"last_name" binding:"required"`
}

The UserIn struct binds the JSON body of a POST /register request. Gin's binding tags reject a request without a valid email, first_name, or last_name.

3

Initialize the Permit client and define the routes

Add the main function to main.go:

// main.go
func main() {
	_ = godotenv.Load()

	apiKey := os.Getenv("PERMIT_API_KEY")
	pdpURL := os.Getenv("PDP_URL")

	permitClient = permit.NewPermit(
		config.NewConfigBuilder(apiKey).
			WithLogger(zap.NewExample()).
			WithPdpUrl(pdpURL).
			Build(),
	)

	router := gin.Default()

	// health check endpoint
	router.GET("/", func(c *gin.Context) {
		c.JSON(http.StatusOK, gin.H{"message": "Hello, Gin with Permit!"})
	})

	// register new user
	router.POST("/register", registerUserHandler)

	// protected endpoint: only authors can create posts
	router.POST("/posts", CreatePostMiddleware(), func(c *gin.Context) {
		c.JSON(http.StatusCreated, gin.H{
			"message": "Post created successfully",
		})
	})

	log.Println("Server running on http://localhost:8000")
	router.Run(":8000")
}

The main function loads a .env file with godotenv, if one exists, and creates the Permit client from two environment variables:

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

The function then registers three routes on port 8000:

Route	Handler
GET /	Returns a health message
POST /register	registerUserHandler
POST /posts	CreatePostMiddleware(), then a handler that returns 201 with "Post created successfully"

4

Add the /register handler

Add registerUserHandler to main.go. The handler syncs the user to Permit.io with permitClient.Api.Users.SyncUser(), then assigns the user the Reader role in the default tenant with permitClient.Api.Users.AssignRole().

// handler for /register endpoint
func registerUserHandler(c *gin.Context) {
	var user UserIn
	if err := c.ShouldBindJSON(&user); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	createUser := models.NewUserCreate(user.Email)
	createUser.SetFirstName(user.FirstName)
	createUser.SetLastName(user.LastName)
	createUser.SetEmail(user.Email)

	newUser, err := permitClient.Api.Users.SyncUser(context.Background(), *createUser)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to sync user"})
		return
	}
	if newUser == nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "User not found"})
		return
	}

	// Assign the Reader role to the user in the 'default' tenant
	roleAssignment, err := permitClient.Api.Users.AssignRole(context.Background(), user.Email, "Reader", "default")
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to assign role"})
		return
	}

	// ... proceed with your app's registration logic
	// For example, create a user record in your database here

	c.JSON(http.StatusCreated, gin.H{
		"message":         "User registered and role assigned",
		"user":            newUser,
		"role_assignment": roleAssignment,
	})
}

The user's email address is the user key in Permit.io. The /posts middleware passes the same key to permitClient.Check().

5

Protect the /posts route with middleware

Add CreatePostMiddleware to main.go. The middleware reads the user key from the X-User header and asks the PDP whether that user can create a Post:

// middleware for checking if the user can create a post
func CreatePostMiddleware() gin.HandlerFunc {
	return func(c *gin.Context) {
		user := c.GetHeader("X-User")
		if user == "" {
			c.JSON(http.StatusBadRequest, gin.H{"error": "Missing permission header: X-User"})
			c.Abort()
			return
		}

		action := "create"
		resource := "Post"

		enfUser := enforcement.UserBuilder(user).Build()
		enfResource := enforcement.ResourceBuilder(resource).Build()

		permitted, err := permitClient.Check(enfUser, enforcement.Action(action), enfResource)
		if err != nil {
			c.JSON(http.StatusInternalServerError, gin.H{"error": "Permission check failed"})
			c.Abort()
			return
		}
		if !permitted {
			c.JSON(http.StatusForbidden, gin.H{"message": "You are not authorized to create a post"})
			c.Abort()
			return
		}
		c.Next()
	}
}

The middleware responds as follows:

Condition	Response
The X-User header is missing	400 with "Missing permission header: X-User"
The PDP call fails	500 with "Permission check failed"
The PDP denies the request	403 with "You are not authorized to create a post"
The PDP allows the request	Gin runs the /posts handler, which returns 201

To protect other routes, such as commenting or editing, change the action and resource values.

note

In a production app, take the user key from your authenticated session. This example reads the user key from the X-User header so that you can test the route with curl.

6

Start the Gin app

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

export PERMIT_API_KEY=<YOUR_API_KEY>
export PDP_URL=http://localhost:7766
go run main.go

The app listens on http://localhost:8000.

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:8000/register \
  -H "Content-Type: application/json" \
  -d '{"email": "john@example.com", "first_name": "John", "last_name": "Doe"}'

curl -X POST http://localhost:8000/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 role assignment under role_assignment, with "role": "Reader" and "tenant": "default".

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:8000/posts \
  -H "X-User: john@example.com"

The PDP allows the request because John has the Author role. The app returns HTTP 201 with {"message":"Post created successfully"}.

Send the same request for Emma:

curl -X POST http://localhost:8000/posts \
  -H "X-User: emma@example.com"

The PDP denies the request because Emma has only the Reader role. The app returns HTTP 403 with {"message":"You are not authorized to create a post"}.

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 Go SDK: SDK installation, configuration, and more permission 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.
• Deploy the PDP to production: run the PDP next to your services.

Next step

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