Authentication and Authorization

Our todo app is nearly functionally complete, but it still doesn't fulfill a very basic requirement - that users should log in before they can view, create or modify tasks.

Remult provides a flexible mechanism that enables placing code-based authorization rules at various levels of the application's API. To maintain high code cohesion, entity and field-level authorization code should be placed in entity classes.

Remult is completely unopinionated when it comes to user authentication. You are free to use any kind of authentication mechanism, and only required to provide Remult with an object which implements the Remult UserInfo interface.

In this tutorial, we'll use Express's cookie-session middleware to store an authenticated user's session within a cookie. The user property of the session will be set by the API server upon a successful simplistic sign-in (based on username without password).

Tasks CRUD Requires Sign-in

This rule is implemented within the Task @Entity decorator, by modifying the value of the allowApiCrud property. This property can be set to a function that accepts a Remult argument and returns a boolean value. Let's use the Allow.authenticated function from Remult.

// src/shared/Task.ts

@Entity("tasks", {
    allowApiCrud: Allow.authenticated
})

Import Allow

This code requires adding an import of Allow from remult.

After the browser refreshes, the list of tasks disappeared and the user can no longer create new tasks.

Inspect the HTTP error returned by the API using cURL

curl -i http://localhost:3002/api/tasks

Authorized server-side code can still modify tasks

Although client CRUD requests to tasks API endpoints now require a signed-in user, the API endpoint created for our setAllCompleted server function remains available to unauthenticated requests. Since the allowApiCrud rule we implemented does not affect the server-side code's ability to use the Task entity class for performing database CRUD operations, the setAllCompleted function still works as before.

To fix this, let's implement the same rule using the @BackendMethod decorator of the setAllCompleted method of TasksController.

// src/shared/TasksController.ts

@BackendMethod({ allowed: Allow.authenticated })

This code requires adding an import of Allow from remult.

User Authentication

Let's add a sign-in area to the todo app, with an input for typing in a username and a sign-in button. The app will have two valid username values - "Jane" and "Steve". After a successful sign-in, the sign-in area will be replaced by a "Hi [username]" message.

Backend setup

1. Open a terminal and run the following command to install the required packages:

npm i cookie-session
npm i --save-dev @types/cookie-session

2. Modify the main server module index.ts to use the cookie-session Express middleware.

   // src/server/index.ts
   
   //...
   
   import session from "cookie-session"
   
   const app = express()
   app.use(
     session({
       secret: process.env["SESSION_SECRET"] || "my secret"
     })
   )
   
   //...

   The cookie-session middleware stores session data, digitally signed using the value of the secret property, in an httpOnly cookie, sent by the browser to all subsequent API requests.

3. Create a file src/server/auth.ts for the auth express router and place the following code in it:

   // src/server/auth.ts
   
   import express, { Router } from 'express'
   import type { UserInfo } from 'remult'
   
   const validUsers: UserInfo[] = [
     { id: '1', name: 'Jane' },
     { id: '2', name: 'Steve' },
   ]
   
   export const auth = Router()
   
   auth.use(express.json())
   
   auth.post('/api/signIn', (req, res) => {
     const user = validUsers.find((user) => user.name === req.body.username)
     if (user) {
       req.session!['user'] = user
       res.json(user)
     } else {
       res.status(404).json("Invalid user, try 'Steve' or 'Jane'")
     }
   })
   
   auth.post('/api/signOut', (req, res) => {
     req.session!['user'] = null
     res.json('signed out')
   })
   
   auth.get('/api/currentUser', (req, res) => res.json(req.session!['user']))

   • The (very) simplistic signIn endpoint accepts a request body with a username property, looks it up in a predefined dictionary of valid users and, if found, sets the user's information to the user property of the request's session.

   • The signOut endpoint clears the user value from the current session.

   • The currentUser endpoint extracts the value of the current user from the session and returns it in the API response.

4. Register the auth router in the main server module.

   // src/server/index.ts
   
   //...
   
   import { auth } from "./auth.js"
   
   const app = express()
   app.use(
     session({
       secret: process.env["SESSION_SECRET"] || "my secret"
     })
   )
   app.use(auth)
   
   //...

Frontend setup

1. Create a file src/Auth.tsx and place the following Auth component code in it:

   // src/Auth.tsx
   
   import { FormEvent, useEffect, useState } from "react"
   import { remult } from "remult"
   import App from "./App"
   
   export default function Auth() {
     const [username, setUsername] = useState("")
     const [signedIn, setSignedIn] = useState(false)
   
     const signIn = async (e: FormEvent) => {
       e.preventDefault()
       const result = await fetch("/api/signIn", {
         method: "POST",
         headers: {
           "Content-Type": "application/json"
         },
         body: JSON.stringify({ username })
       })
       if (result.ok) {
         remult.user = await result.json()
         setSignedIn(true)
         setUsername("")
       } else {
         alert(await result.json())
       }
     }
   
     const signOut = async () => {
       await fetch("/api/signOut", {
         method: "POST"
       })
       remult.user = undefined
       setSignedIn(false)
     }
     useEffect(() => {
       fetch("/api/currentUser").then(async r => {
         remult.user = await r.json()
         if (remult.user) setSignedIn(true)
       })
     }, [])
   
     if (!signedIn)
       return (
         <>
           <h1>Todos</h1>
           <main>
             <form onSubmit={signIn}>
               <input
                 value={username}
                 onChange={e => setUsername(e.target.value)}
                 placeholder="Username, try Steve or Jane"
               />
               <button>Sign in</button>
             </form>
           </main>
         </>
       )
     return (
       <>
         <header>
           Hello {remult.user!.name} <button onClick={signOut}>Sign Out</button>
         </header>
         <App />
       </>
     )
   }

2. In the main.tsx file, Replace the App component with the Auth component.

   // src/main.tsx
   
   import React from "react"
   import ReactDOM from "react-dom/client"
   import Auth from "./Auth"
   import "./index.css"
   
   ReactDOM.createRoot(document.getElementById("root") as HTMLElement).render(
     <React.StrictMode>
       <Auth />
     </React.StrictMode>
   )

Connect Remult middleware

Once an authentication flow is established, integrating it with Remult in the backend is as simple as providing Remult with a getUser function that extracts a UserInfo object from a Request.

// src/server/api.ts

//...

export const api = remultExpress({
  //...
  getUser: req => req.session!["user"]
})

The todo app now supports signing in and out, with all access restricted to signed in users only.

Role-based Authorization

Usually, not all application users have the same privileges. Let's define an admin role for our todo app, and enforce the following authorization rules:

• All signed in users can see the list of tasks.
• All signed in users can set specific tasks as completed.
• Only users belonging to the admin role can create, delete or edit the titles of tasks.

1. Modify the highlighted lines in the Task entity class to reflect the top three authorization rules.

// src/shared/Task.ts

import { Allow, Entity, Fields, Validators } from "remult"

@Entity<Task>("tasks", {
  allowApiCrud: Allow.authenticated,
  allowApiInsert: "admin",
  allowApiDelete: "admin"
})
export class Task {
  @Fields.uuid()
  id!: string

  @Fields.string({
    validate: (task) => {
      if (task.title.length < 3) throw "Too Short"
    }
    allowApiUpdate: "admin"
  })
  title = ""

  @Fields.boolean()
  completed = false
}

2. Let's give the user "Jane" the admin role by modifying the roles array of her validUsers entry.

// src/server/auth.ts

const validUsers = [
  { id: "1", name: "Jane", roles: ["admin"] },
  { id: "2", name: "Steve" }
]

Sign in to the app as "Steve" to test that the actions restricted to admin users are not allowed. 🔒

Role-based Authorization on the Frontend

From a user experience perspective it only makes sense that users that can't add or delete, would not see these buttons.

Let's reuse the same definitions on the Frontend.

We'll use the entity's metadata to only show the form if the user is allowed to insert

// src/App.tsx

<main>
  {taskRepo.metadata.apiInsertAllowed() && (
    <form onSubmit={addTask}>
      <input
        value={newTaskTitle}
        placeholder="What needs to be done?"
        onChange={e => setNewTaskTitle(e.target.value)}
      />
      <button>Add</button>
    </form>
  )}
  ...
</main>

And let's do the same for the delete button:

// src/App.tsx

return (
  <div key={task.id}>
    <input
      type="checkbox"
      checked={task.completed}
      onChange={e => setCompleted(e.target.checked)}
    />
    <input value={task.title} onChange={e => setTitle(e.target.value)} />
    <button onClick={saveTask}>Save</button>
    {taskRepo.metadata.apiDeleteAllowed(task) && (
      <button onClick={deleteTask}>Delete</button>
    )}
  </div>
)

This way we can keep the frontend consistent with the api's Authorization rules

• Note We send the task to the apiDeleteAllowed method, because the apiDeleteAllowed option, can be sophisticated and can also be based on the specific item's values.