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Access Control ​

Access control is essential for ensuring that users can only access resources they are authorized to in web applications. This article explores the various layers of access control, focusing on a framework that provides a granular approach to securing your application.

Entity-Level Authorization ​

Entity-level authorization governs CRUD (Create, Read, Update, Delete) operations at the entity level. Each entity can define permissions for these operations using the following options:

  • allowApiRead: Controls read access.
  • allowApiInsert: Controls insert access.
  • allowApiUpdate: Controls update access.
  • allowApiDelete: Controls delete access.

Each option can be set to a boolean, a string role, an array of string roles, or an arrow function:

typescript
// Allows all CRUD operations
@Entity("tasks", { allowApiCrud: true })

// Only users with the 'admin' role can update
@Entity("tasks", { allowApiUpdate: 'admin' })

// Only users with 'admin' or 'manager' roles can delete
@Entity("tasks", { allowApiDelete: ['admin', 'manager'] })

// Only the user 'Jane' can read
@Entity("tasks", { allowApiRead: () => remult.user?.name == 'Jane' })

// Only authenticated users can perform CRUD operations
@Entity("tasks", { allowApiCrud: Allow.authenticated })

Row-Level Authorization ​

Row-level authorization allows control over which rows a user can access or modify.

Authorization on Specific Rows ​

The allowApiUpdate, allowApiDelete, and allowApiInsert options can also accept a function that receives the specific item as the first parameter, allowing row-level authorization:

ts
// Users can only update tasks they own
@Entity<Task>("tasks", { allowApiUpdate: task => task.owner == remult.user?.id })

Filtering Accessible Rows ​

To limit the rows a user has access to, use the apiPrefilter option:

ts
@Entity<Task>("tasks", {
  apiPrefilter: () => {
    // Admins can access all rows
    if (remult.isAllowed("admin")) return {}
    // Non-admins can only access rows where they are the owner
    return { owner: remult.user!.id }
  }
})

The apiPrefilter adds a filter to all CRUD API requests, ensuring that only authorized data is accessible through the API.

Preprocessing Filters for API Requests ​

For more complex scenarios, you can use apiPreprocessFilter to dynamically modify the filter based on the specific request and additional filter information:

ts
@Entity<Task>("tasks", {
  apiPreprocessFilter: async (filter, {getPreciseValues}) => {
    // Ensure that users can only query tasks for specific customers
    const preciseValues = await getPreciseValues();
    if (!preciseValues.customerId) {
      throw new ForbiddenError("You must specify a valid customerId filter");
    }
    return filter;
  }
})

In this example, apiPreprocessFilter uses the getPreciseValues method to ensure that users must specify a valid customerId filter when querying tasks, allowing for more granular control over the data that is accessible through the API.

Note: The preciseValues object includes the actual values that are used in the filter. For example, in the code sample above, if the customerId filter specifies the values '1', '2', and '3', then preciseValues.customerId will be an array containing these values. This allows you to check and enforce specific filter criteria in your preprocessing logic.

This added note explains the significance of the preciseValues property and how it includes the actual values used in the filter, providing an example for clarity.

Warning: API Filters Do Not Affect Backend Queries ​

It's important to note that apiPrefilter and apiPreprocessFilter only apply to API requests. They do not affect backend queries, such as those executed through backend methods or non-Remult routes.

For instance, in a sign-in scenario, a backend method might need to check all user records to verify a user's existence without exposing all user data through the API. Once authenticated, the user should only have access to their own record for updates.

Backend Filters for Consistent Access Control ​

To apply similar filtering logic to backend queries, you can use backendPrefilter and backendPreprocessFilter:

ts
@Entity<Task>("tasks", {
  backendPrefilter: () => {
    // Admins can access all rows
    if (remult.isAllowed("admin")) return {}
    // Non-admins can only access rows where they are the owner
    return { owner: remult.user!.id }
  },
  backendPreprocessFilter: async (filter, {getPreciseValues}) => {
    // Apply additional filtering logic for backend queries
    const preciseValues = await getPreciseValues(filter);
    if (!preciseValues.owner) {
      throw new ForbiddenError("You must specify a valid owner filter");
    }
    return filter;
  }
})

In this example, backendPrefilter and backendPreprocessFilter ensure that non-admin users can only access their own tasks in backend queries, providing consistent access control across both API and backend operations.

Field-Level Authorization ​

Field-level authorization allows control over individual fields within an entity:

  • includeInApi: Determines if the field is included in the API response.
  • allowApiUpdate: Controls if a field can be updated. If false, any change to the field is ignored.

Examples:

ts
// This field will not be included in the API response
@Fields.string({ includeInApi: false })
password = ""

// Only users with the 'admin' role can update this field
@Fields.boolean({ allowApiUpdate: "admin" })
admin = false

// Titles can only be updated by the task owner
@Fields.string<Task>({ allowApiUpdate: task => task.owner === remult.user!.id })
title=''

// This field can only be updated when creating a new entity
@Fields.string<Category>({ allowApiUpdate: (c) => getEntityRef(c).isNew() })
Description = ""

Field Masking ​

To mask a field, combine a non-API field with a serverExpression that returns the masked value:

ts
// This field is not included in the API response
@Fields.string({ includeInApi: false })
password = ""

// The field value is masked in the API response
@Fields.string<User>({
  serverExpression: () => "***",
  // Update the real password field when the masked field is changed
  saving: async (user, fieldRef, e) => {
    if (fieldRef.valueChanged()) {
      user.password = await User.hash(user.updatePassword)
    }
  },
})
updatePassword = ""

BackendMethod Authorization ​

Backend methods use the allowed option to determine authorization:

ts
// Only authenticated users can execute this method
@BackendMethod({ allowed: Allow.authenticated })
static async doSomething() {
  // something
}

The allowed option can receive a boolean, a string role, an array of role strings, or a function.

Reusing Access Control Definitions in the Frontend ​

Access control definitions set in entities can be reused as a single source of truth in the frontend. This allows for consistent and centralized management of access control logic across your application. For example, in a React component, you can conditionally render UI elements based on the access control rules defined in the entity:

tsx
function UserComponent({ user }: { user: User }) {
  //...
  return (
    <tr>
      <td>{user.name}</td>
      {/* Only show the admin field if the user is allowed to see it */}
      {userRepo.fields.admin.includeInApi(user) && <td>{user.admin}</td>}
      {/* Only show the delete button if the user is allowed to delete the admin */}
      {userRepo.metadata.apiDeleteAllowed(user) && (
        <td>
          <button onClick={deleteUser}>Delete</button>
        </td>
      )}
    </tr>
  )
}
html
<tr>
  <td>{{user.name}}</td>
  <!-- Only show the admin field if the user is allowed to see it -->
  <td *ngIf="userRepo.fields.admin.includeInApi(user)">{{user.admin}}</td>
  <!-- Only show the delete button if the user is allowed to delete the admin-->
  <td *ngIf="userRepo.metadata.apiDeleteAllowed(user)">
    <button (click)="deleteUser(user)">Delete</button>
  </td>
</tr>
vue
<tr>
  <td>{{user.name}}</td>
  <!-- Only show the admin field if the user is allowed to see it -->
  <td v-if="userRepo.fields.admin.includeInApi(user)">{{user.admin}}</td>
  <!-- Only show the delete button if the user is allowed to delete the admin-->
  <td v-if="userRepo.metadata.apiDeleteAllowed(user)">
    <button @click="deleteUser(user)">Delete</button>
  </td>
</tr>
svelte
<tr>
  <td>{{user.name}}</td>
  <!-- Only show the admin field if the user is allowed to see it -->
  {#if userRepo.fields.admin.includeInApi(user)}
  <td>{{user.admin}}</td>
  {/if}
  <!-- Only show the delete button if the user is allowed to delete the admin-->
  {#if userRepo.metadata.apiDeleteAllowed(user)}
  <td>
    <button (click)="deleteUser(user)">Delete</button>
  </td>
  {/if}
</tr>

Additional Resources ​

Check out this informative YouTube video. It discusses the concepts covered in this article and provides practical examples to help you understand how to implement robust access control in your applications.

This article provides a comprehensive overview of the layers of access control in web applications, offering a granular approach to securing your application at the entity, row, field, and method levels.

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