Interceptors for authentication tokens in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an HTTP interceptor in Angular?

An HTTP interceptor is a service that can inspect and transform HTTP requests or responses globally before they reach the server or the app. It helps add headers, handle errors, or modify requests centrally.

beginner

Why use an interceptor for authentication tokens?

Using an interceptor lets you automatically add authentication tokens to every HTTP request without repeating code in each service. This keeps your code clean and secure.

intermediate

How do you provide an interceptor in Angular?

You provide an interceptor by adding it to the providers array with the token HTTP_INTERCEPTORS and setting multi: true. This tells Angular to use your interceptor alongside others.

intermediate

What method must an Angular interceptor implement?

An Angular interceptor must implement the intercept(req, next) method. It receives the outgoing request and the next handler, and returns an Observable of the HTTP event.

advanced

How can you handle token expiration in an interceptor?

You can check the server response for 401 errors in the interceptor, then trigger a token refresh or redirect to login. This centralizes token expiration handling.

What does an Angular HTTP interceptor primarily do?

A Create new HTTP requests manually

B Handle UI events

C Replace Angular services

D Modify HTTP requests and responses globally

Interceptors modify HTTP requests and responses before they reach the server or the app.

How do you add an interceptor to Angular's HTTP pipeline?

A Import it in the component directly

B Add it to the providers array with HTTP_INTERCEPTORS and multi: true

C Call it inside each service method

D Declare it in the module's declarations

Interceptors must be provided with HTTP_INTERCEPTORS token and multi: true in providers.

Which method must be implemented in an Angular HTTP interceptor?

A intercept(req, next)

B handleRequest()

C sendRequest()

D processHttp()

The intercept method handles the request and forwards it.

What is a common use of interceptors in authentication?

A Add authentication tokens to HTTP headers

B Encrypt the entire HTTP request body

C Create new user accounts

D Render login forms

Interceptors add tokens to headers to authenticate requests.

How can an interceptor respond to a 401 Unauthorized error?

A Reload the entire app

B Ignore the error silently

C Trigger token refresh or redirect to login

D Automatically approve the request

Interceptors can catch 401 errors to refresh tokens or redirect users.

Explain how an Angular HTTP interceptor can be used to add authentication tokens to requests.

Think about modifying the request before sending it.

Describe how you would handle expired tokens using an Angular interceptor.

Focus on response handling inside the interceptor.