Federated authentication in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main purpose of federated authentication?

Choose the best description of federated authentication.

A It stores all user passwords in a single database for easy access.

B It encrypts user data locally on their device before sending it to the server.

C It requires users to create new accounts for every service they use.

D It allows users to log in using credentials from multiple trusted identity providers.

💡 Hint

Think about how users can use one login for many services.

Federated authentication lets users sign in with one account from a trusted provider, like Google or Facebook, to access multiple services without creating new passwords.

❓ query_result

intermediate

What is the output of this GraphQL query for federated user info?

Given this GraphQL query requesting user email and provider, what is the expected JSON response?

GraphQL

query {
  user(id: "123") {
    email
    authProvider
  }
}

A { "data": { "user": { "email": "[e-mail]", "authProvider": "Google" } } }

B { "data": { "user": { "email": null, "authProvider": null } } }

C { "error": "User not found" }

D { "data": { "user": { "email": "[e-mail]" } } }

💡 Hint

The user exists and uses Google as their login provider.

The query requests both email and authProvider fields. The user exists, so both fields return valid values.

📝 Syntax

advanced

Which GraphQL schema snippet correctly defines a federated user type with an external key?

Select the valid GraphQL SDL code that defines a federated User type with an external key.

A

type User @key(fields: "id") {
  id: ID!
  email: String
  authProvider: String
}

B

type User @external(fields: "id") {
  id: ID!
  email: String
  authProvider: String
}

C

type User @key(fields: id) {
  id: ID!
  email: String
  authProvider: String
}

D

type User @key(fields: "id") {
  id: ID
  email: String
  authProvider: String
}

💡 Hint

The @key directive requires quoted field names and non-null id.

The @key directive must have quoted field names. The id field must be non-nullable (ID!). Option A follows both rules.

❓ optimization

advanced

How to optimize federated GraphQL queries to reduce data fetching overhead?

Which approach best reduces unnecessary data fetching in a federated GraphQL service?

A Fetch all fields from every service regardless of query to cache data.

B Disable query batching to send each request separately for clarity.

C Use @requires directive to specify dependent fields and avoid fetching unrelated data.

D Use multiple nested queries to fetch data from each service independently.

💡 Hint

Think about how to tell the gateway what fields are needed for resolving.

The @requires directive helps specify which fields are needed from other services, so the gateway fetches only necessary data, improving efficiency.

🔧 Debug

expert

Why does this federated GraphQL query fail with a 'Cannot query field' error?

Given this query: query { user(id: "123") { id email profilePicture } } And the User type schema: type User @key(fields: "id") { id: ID! email: String } Why does querying profilePicture cause an error?

A The id field is missing from the query, causing the error.

B The profilePicture field is not defined in the User type schema, so it cannot be queried.

C The @key directive is incorrectly used and causes all fields to be inaccessible.

D The user id "123" does not exist, so no fields can be queried.

💡 Hint

Check if the requested field exists in the schema.

The error occurs because profilePicture is not declared in the User type schema, so GraphQL rejects the query for that field.