GraphQL is a powerful query language for APIs that allows clients to request specific data fields. In a GraphQL server, it is common to have various access control requirements to restrict certain fields based on user permissions. In this blog post, we will explore how to implement field-level access control in a JavaScript GraphQL server using role-based authorization.

Setting Up the GraphQL Server

Before we dive into implementing access control, let’s set up a basic GraphQL server in JavaScript. We’ll use the popular graphql-yoga library for this example.

First, make sure you have Node.js installed on your machine. Then, create a new directory, navigate to it in the terminal, and run the following commands:

npm init -y
npm install graphql-yoga

Next, create a new file named index.js and add the following code:

const { GraphQLServer } = require('graphql-yoga');

const typeDefs = `
  type Query {
    publicField: String!
    privateField: String!
  }
`;

const resolvers = {
  Query: {
    publicField: () => 'This is a public field',
    privateField: () => 'This is a private field',
  },
};

const server = new GraphQLServer({
  typeDefs,
  resolvers,
});

server.start(() => {
  console.log('GraphQL server is running on localhost:4000');
});

In this basic setup, we have defined a GraphQL schema with two fields: publicField and privateField. The publicField is accessible to all users, while the privateField should only be accessible to authorized users.

Implementing Field-Level Access Control

To implement field-level access control, we will introduce the concept of roles. Each user will be assigned one or more roles, which determine their level of access to different fields in the schema.

First, let’s update the typeDefs to include roles for each field:

const typeDefs = `
  type Query {
    publicField: String!
    privateField: String! @auth(roles: [ADMIN])
  }

  enum Role {
    ADMIN
    USER
  }
`;

In this example, we have added the @auth directive to the privateField and specified that it requires the role ADMIN.

Next, we need to define a middleware function that checks the user’s role and determines whether they have access to the requested field. Add the following code after the typeDefs:

const isAuthenticated = (resolver, parent, args, ctx, info) => {
  // Check if user is authenticated and has the necessary role
  if (!ctx.user || !ctx.user.roles.includes('ADMIN')) {
    throw new Error('You are not authorized to access this field');
  }

  return resolver(parent, args, ctx, info);
};

const resolvers = {
  Query: {
    publicField: () => 'This is a public field',
    privateField: isAuthenticated(() => 'This is a private field'),
  },
};

Here, we have defined the isAuthenticated middleware function which takes a resolver function as an argument. Within this function, we check if the user is authenticated and has the necessary role. If not, we throw an error indicating that they are not authorized. If the user is authenticated and has the correct role, we call the resolver function to fetch the data for the field.

Testing Access Control

To test our field-level access control, we need to provide the necessary user information and roles to the GraphQL server. We can do this by updating the server.start() function call:

server.start({
  context: {
    user: {
      roles: ['ADMIN'],
    },
  },
}, () => {
  console.log('GraphQL server is running on localhost:4000');
});

In this example, we have provided a dummy user object with the role ADMIN.

Now, if you run the GraphQL server and make a query to the privateField, you should see the expected result:

{
  privateField
}

If you remove or change the role of the user, you will receive an error indicating that you are not authorized to access the field.

Conclusion

Implementing field-level access control in a JavaScript GraphQL server is essential for securing sensitive data and ensuring that only authorized users can access certain fields. By leveraging roles and middleware functions, we can easily define and enforce access control rules in our GraphQL schema.

Remember to always consider security best practices when implementing access control and handle sensitive data with care. Happy coding!

#GraphQL #JavaScript