Authentication errors in context in GraphQL - Mini Project: Build & Apply

Handling Authentication Errors in GraphQL Context

📖 Scenario: You are building a GraphQL API for a simple blog platform. Users must be authenticated to create posts. You want to handle authentication errors properly by using the GraphQL context to check if a user is logged in before allowing post creation.

🎯 Goal: Build a GraphQL schema and resolver setup that checks for user authentication in the context and returns an authentication error if the user is not logged in.

📋 What You'll Learn

Create a GraphQL schema with a Mutation type that has a createPost field accepting title and content arguments.

Add a context object that contains a user field representing the logged-in user or null if not logged in.

In the resolver for createPost, check if context.user exists; if not, throw an authentication error.

Return the created post object with id, title, content, and author fields.

💡 Why This Matters

🌍 Real World

Handling authentication errors in GraphQL APIs is essential for protecting sensitive operations like creating posts or accessing user data.

💼 Career

Understanding how to use context for authentication and error handling is a key skill for backend developers working with GraphQL.

1

Define the GraphQL schema with Post type and createPost mutation

Write the GraphQL schema defining a Post type with fields id, title, content, and author. Also define a Mutation type with a createPost field that accepts title and content as String! arguments and returns a Post.

GraphQL

# Define the GraphQL schema with Post type and createPost mutation
# Your code here

Hint

Define the Post type first, then add the createPost mutation with the correct arguments and return type.

2

Add context object with user field

In your GraphQL server setup, create a context object that includes a user field. Set user to null to simulate no logged-in user for now.

GraphQL

type Post {
  id: ID!
  title: String!
  content: String!
  author: String!
}

type Mutation {
  createPost(title: String!, content: String!): Post
}

const context = {
  // Your code here
}

Hint

Define a context object with a user property set to null.

3

Implement createPost resolver with authentication check

Write the resolver function for createPost that accepts parent, args, and context. Check if context.user is null. If so, throw an error with the message Authentication required. Otherwise, return a new post object with id set to "1", title and content from args, and author from context.user.

GraphQL

type Post {
  id: ID!
  title: String!
  content: String!
  author: String!
}

type Mutation {
  createPost(title: String!, content: String!): Post
}

const context = {
  user: null
}

const resolvers = {
  Mutation: {
    createPost(parent, args, context) {
      // Your code here
    }
  }
}

Hint

Check context.user and throw an error if missing. Otherwise, return the post object with the correct fields.

4

Set context user to simulate logged-in user

Modify the context object to set user to the string "Alice" to simulate a logged-in user named Alice.

GraphQL

type Post {
  id: ID!
  title: String!
  content: String!
  author: String!
}

type Mutation {
  createPost(title: String!, content: String!): Post
}

const context = {
  // Your code here
}

const resolvers = {
  Mutation: {
    createPost(parent, args, context) {
      if (!context.user) {
        throw new Error('Authentication required');
      }
      return {
        id: '1',
        title: args.title,
        content: args.content,
        author: context.user
      };
    }
  }
}

Hint

Set user in context to 'Alice'.