Directive-based authorization in GraphQL - Mini Project: Build & Apply

Directive-based Authorization in GraphQL

📖 Scenario: You are building a GraphQL API for a simple blog platform. You want to control access to certain fields and operations based on user roles using directive-based authorization.

🎯 Goal: Create a GraphQL schema that uses a custom @auth directive to restrict access to fields and queries based on user roles.

📋 What You'll Learn

Define a custom directive called @auth that accepts a role argument.

Create a User type with fields id, username, and email.

Create a Query type with a field users that returns a list of User.

Apply the @auth(role: "ADMIN") directive to the users query to restrict it to admin users.

Apply the @auth(role: "USER") directive to the email field to restrict email visibility to users with the USER role.

💡 Why This Matters

🌍 Real World

Directive-based authorization is commonly used in GraphQL APIs to control access to data based on user roles or permissions.

💼 Career

Understanding how to implement and use custom directives for authorization is valuable for backend developers working with GraphQL APIs.

1

Define the @auth directive and User type

Create a GraphQL schema that defines a directive called @auth which takes a role argument of type String!. Also, define a User type with fields id of type ID!, username of type String!, and email of type String!.

GraphQL

# Define the @auth directive and User type
# Your code here

Hint

Use the directive keyword to define @auth with a role argument. Then define the User type with the specified fields.

2

Add the Query type with users field

Add a Query type to the schema with a field called users that returns a list of User (use [User!]! as the return type).

GraphQL

directive @auth(role: String!) on FIELD_DEFINITION | OBJECT

type User {
  id: ID!
  username: String!
  email: String!
}

# Add Query type with users field
# Your code here

Hint

Define the Query type and add the users field returning a non-null list of non-null User objects.

3

Apply @auth(role: "ADMIN") directive to users query

Modify the users field in the Query type to include the @auth(role: "ADMIN") directive to restrict access to admin users only.

GraphQL

directive @auth(role: String!) on FIELD_DEFINITION | OBJECT

type User {
  id: ID!
  username: String!
  email: String!
}

type Query {
  # Add @auth directive to users field
  users: [User!]!
}

Hint

Add the @auth(role: "ADMIN") directive right after the users field type declaration.

4

Apply @auth(role: "USER") directive to email field

Modify the email field in the User type to include the @auth(role: "USER") directive to restrict email visibility to users with the USER role.

GraphQL

directive @auth(role: String!) on FIELD_DEFINITION | OBJECT

type User {
  id: ID!
  username: String!
  # Add @auth directive to email field
  email: String!
}

type Query {
  users: [User!]! @auth(role: "ADMIN")
}

Hint

Add the @auth(role: "USER") directive immediately after the email field type.

Practice

1. What is the main purpose of using directive-based authorization in GraphQL?

easy

A. To control who can access certain data or operations

B. To speed up query execution

C. To format the output data

D. To create new database tables

Solution

1. Step 1: Understand directive-based authorization

   Directive-based authorization adds rules to GraphQL fields or types to restrict access based on user roles or permissions.

2. Step 2: Identify the main goal

   The main goal is to control access to data or operations, ensuring only authorized users can see or change certain information.

3. Final Answer:

   To control who can access certain data or operations -> Option A

4. Quick Check:

   Authorization controls access = B [OK]

Hint: Authorization directives control access permissions [OK]

Common Mistakes:

• Confusing authorization with performance optimization
• Thinking directives format data output
• Assuming directives create database structures

2. Which of the following is the correct syntax to apply a directive named @auth requiring a role ADMIN on a GraphQL field?

easy

A. type Query { secretData: String @auth(role: ADMIN) }

B. type Query { secretData: String @auth(role: "ADMIN") }

C. type Query { secretData: String @auth(role=ADMIN) }

D. type Query { secretData: String @auth[role=ADMIN] }

Solution

1. Step 1: Recall directive syntax in GraphQL

   Directives use parentheses with named arguments and string values in quotes, e.g., @directiveName(argName: "value").

2. Step 2: Match the correct syntax

   type Query { secretData: String @auth(role: "ADMIN") } correctly uses @auth(role: "ADMIN") with quotes around the string role value.

3. Final Answer:

   type Query { secretData: String @auth(role: "ADMIN") } -> Option B

4. Quick Check:

   Directive args use parentheses and quotes = D [OK]

Hint: Directives use parentheses and quoted strings for arguments [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting quotes around string values
• Using equals sign without quotes

3. Given the schema snippet:

type Query {
  userProfile: User @auth(role: "USER")
}

type User {
  id: ID!
  email: String
  secretNote: String @auth(role: "ADMIN")
}

What happens when a user with role USER queries userProfile { id email secretNote }?

medium

A. The query returns only id

B. The query returns all fields including secretNote

C. The query fails with an authorization error

D. The query returns id and email, but secretNote is blocked

Solution

1. Step 1: Analyze field-level directives

   The userProfile field requires role USER, so the user can access it. The secretNote field requires ADMIN role, which the user does not have.

2. Step 2: Determine accessible fields

   The user can see id and email but not secretNote because of the stricter ADMIN directive on that field.

3. Final Answer:

   The query returns id and email, but secretNote is blocked -> Option D

4. Quick Check:

   Field directives restrict access individually = C [OK]

Hint: Field directives override parent access; check each field's role [OK]

Common Mistakes:

• Assuming all fields inherit parent directive permissions
• Expecting full data without role ADMIN
• Thinking query fails instead of partial data

4. Consider this schema snippet:

type Query {
  adminData: String @auth(role: "ADMIN")
}

Which of the following fixes the error if the directive @auth is not recognized by the GraphQL server?

medium

A. Define the @auth directive in the schema with directive @auth(role: String) on FIELD_DEFINITION

B. Remove the @auth directive from the schema

C. Change @auth to @authorize without defining it

D. Rename the field adminData to adminInfo

Solution

1. Step 1: Understand directive registration

   GraphQL requires custom directives to be declared in the schema before use, specifying their name, arguments, and locations.

2. Step 2: Apply correct fix

   Define the @auth directive in the schema with directive @auth(role: String) on FIELD_DEFINITION correctly defines the @auth directive with a role argument and usage on field definitions, enabling the server to recognize it.

3. Final Answer:

   Define the @auth directive in the schema with directive @auth(role: String) on FIELD_DEFINITION -> Option A

4. Quick Check:

   Custom directives must be declared in schema = A [OK]

Hint: Declare custom directives in schema before use [OK]

Common Mistakes:

• Removing directives without replacing authorization
• Using undefined directive names
• Changing field names unrelated to directive errors

5. You want to restrict access so that only users with role EDITOR or ADMIN can update posts. Which directive usage correctly applies this logic on the updatePost mutation?

hard

A. type Mutation { updatePost(id: ID!, content: String!): Post @auth(role: "EDITOR") @auth(role: "ADMIN") }

B. type Mutation { updatePost(id: ID!, content: String!): Post @auth(roles: ["EDITOR", "ADMIN"]) }

C. type Mutation { updatePost(id: ID!, content: String!): Post @auth(role_in: ["EDITOR", "ADMIN"]) }

D. type Mutation { updatePost(id: ID!, content: String!): Post @auth(role: "EDITOR" OR "ADMIN") }

Solution

1. Step 1: Understand role list syntax in directives

   To allow multiple roles, the directive argument should accept a list (array) of roles, often named role_in or similar, depending on implementation.

2. Step 2: Evaluate options for correct syntax

   type Mutation { updatePost(id: ID!, content: String!): Post @auth(role_in: ["EDITOR", "ADMIN"]) } uses @auth(role_in: ["EDITOR", "ADMIN"]), which correctly passes an array of roles to check for authorization.

3. Final Answer:

   type Mutation { updatePost(id: ID!, content: String!): Post @auth(role_in: ["EDITOR", "ADMIN"]) } -> Option C

4. Quick Check:

   Use array argument for multiple roles = A [OK]

Hint: Use array argument to list multiple allowed roles [OK]

Common Mistakes:

• Stacking multiple @auth directives instead of one with list
• Using invalid OR syntax inside directive argument
• Using wrong argument name like roles instead of role_in