API authentication patterns in Svelte - Mini Project: Build & Apply

API Authentication Patterns in Svelte

📖 Scenario: You are building a simple Svelte app that needs to authenticate users by sending an API token with requests. This is common when apps talk to servers that require a secret key to allow access.

🎯 Goal: Create a Svelte component that stores an API token, sets a configuration variable for the token header name, uses the token in a fetch request, and finally adds the token to the request headers to authenticate the API call.

📋 What You'll Learn

Create a variable to hold the API token string

Create a configuration variable for the header name

Use the token in a fetch request with the correct header

Add the header to the fetch options to complete the authentication

💡 Why This Matters

🌍 Real World

Many web apps need to authenticate API requests with tokens to access protected data or services.

💼 Career

Understanding how to send authentication headers in fetch requests is essential for frontend developers working with APIs.

1

Set up the API token variable

Create a variable called apiToken and set it to the string "12345abcde" inside the <script> tag.

Svelte

  // Create the apiToken variable here

Hint

Use let apiToken = "12345abcde"; inside the script tag.

2

Add a configuration variable for the header name

Inside the <script> tag, create a variable called authHeader and set it to the string "Authorization".

Svelte

  let apiToken = "12345abcde";
  // Create the authHeader variable here

Hint

Use let authHeader = "Authorization"; to store the header name.

3

Use the token in a fetch request

Inside the <script> tag, create an async function called fetchData that calls fetch with the URL "https://api.example.com/data" and includes the Authorization header with the apiToken value.

Svelte

  let apiToken = "12345abcde";
  let authHeader = "Authorization";

  // Create async function fetchData to fetch with auth header

Hint

Use fetch with a headers object that sets [authHeader] to `Bearer ${apiToken}`.

4

Add a button to trigger the fetch with authentication

Add a <button> element with the text "Load Data" that calls the fetchData function when clicked inside the component markup.

Svelte

  let apiToken = "12345abcde";
  let authHeader = "Authorization";

  async function fetchData() {
    const response = await fetch("https://api.example.com/data", {
      headers: {
        [authHeader]: `Bearer ${apiToken}`
      }
    });
    const data = await response.json();
    return data;
  }

Hint

Use <button on:click={fetchData}>Load Data</button> to trigger the fetch.

Practice

1. What is the main purpose of API authentication in a Svelte app?

easy

A. To verify the identity of the user or app making the request

B. To speed up the API response time

C. To change the API data format

D. To style the API response

Solution

1. Step 1: Understand API authentication role

   API authentication checks who is making the request to keep the app secure.

2. Step 2: Identify the correct purpose

   Speed, data format, and styling are unrelated to authentication.

3. Final Answer:

   To verify the identity of the user or app making the request -> Option A

4. Quick Check:

   Authentication = Verify identity [OK]

Hint: Authentication means checking who you are [OK]

Common Mistakes:

• Confusing authentication with performance optimization
• Thinking authentication changes data format
• Assuming authentication styles the response

2. Which of the following is the correct way to add a Bearer token in a fetch request header in Svelte?

easy

A. fetch(url, { headers: { 'Bearer': token } })

B. fetch(url, { headers: { 'Auth': 'Bearer ' + token } })

C. fetch(url, { headers: { 'Authorization': 'Bearer ' + token } })

D. fetch(url, { headers: { 'Authorization': token } })

Solution

1. Step 1: Recall Bearer token header format

   The standard header key is 'Authorization' with value 'Bearer ' plus the token.

2. Step 2: Match correct syntax

   fetch(url, { headers: { 'Authorization': 'Bearer ' + token } }) correctly uses 'Authorization' and concatenates 'Bearer ' with the token.

3. Final Answer:

   fetch(url, { headers: { 'Authorization': 'Bearer ' + token } }) -> Option C

4. Quick Check:

   Bearer token header = Authorization: Bearer token [OK]

Hint: Use 'Authorization' header with 'Bearer ' prefix [OK]

Common Mistakes:

• Using wrong header key like 'Auth' or 'Bearer'
• Omitting 'Bearer ' prefix before token
• Passing token without header key

3. What will be the output of this Svelte code snippet when fetching an API with Basic Auth?

const response = await fetch('https://api.example.com/data', {
  headers: {
    'Authorization': 'Basic ' + btoa('user:pass')
  }
});
const data = await response.json();
console.log(data.message);

Assuming the API returns {"message": "Success"} on correct auth.

medium

A. SyntaxError

B. Success

C. Authorization error

D. undefined

Solution

1. Step 1: Understand Basic Auth header

   The code correctly encodes 'user:pass' with btoa and sets 'Authorization' header.

2. Step 2: Predict API response

   With correct credentials, API returns JSON with message 'Success', logged to console.

3. Final Answer:

   Success -> Option B

4. Quick Check:

   Correct Basic Auth returns API success message [OK]

Hint: Basic Auth uses base64 encoded 'user:pass' in Authorization [OK]

Common Mistakes:

• Not encoding credentials with btoa
• Using wrong header key
• Expecting error without wrong credentials

4. Identify the error in this Svelte fetch call for API authentication:

fetch('https://api.example.com/data', {
  headers: {
    'Authorization': 'Bearer token123'
  }
})
.then(response => response.json())
.then(data => console.log(data));

medium

A. Missing await keyword for async fetch

B. Bearer token should be in lowercase

C. Headers object should be outside fetch options

D. No error, code is correct

Solution

1. Step 1: Check fetch usage with promises

   Using .then() is valid without await; async/await is optional here.

2. Step 2: Verify header format and placement

   'Authorization' header with 'Bearer token123' is correct and inside headers object.

3. Final Answer:

   No error, code is correct -> Option D

4. Quick Check:

   fetch with .then and correct headers = valid code [OK]

Hint: Using .then() is valid without await [OK]

Common Mistakes:

• Thinking await is mandatory with fetch
• Assuming 'Bearer' must be lowercase
• Misplacing headers outside fetch options

5. You want to securely store and use an API token in a Svelte app to authenticate requests. Which approach is best practice?

hard

A. Store the token in a Svelte writable store and include it in fetch headers

B. Hardcode the token directly in the fetch call inside the component

C. Save the token in localStorage and read it on every fetch request

D. Send the token as a URL query parameter in fetch requests

Solution

1. Step 1: Evaluate token storage options

   Writable stores in Svelte keep token in memory, safer than localStorage or hardcoding.

2. Step 2: Assess token usage in fetch

   Including token in headers from store is secure and flexible; URL query parameters expose token publicly.

3. Final Answer:

   Store the token in a Svelte writable store and include it in fetch headers -> Option A

4. Quick Check:

   Use writable store for secure token handling [OK]

Hint: Use Svelte stores, avoid hardcoding or URL tokens [OK]

Common Mistakes:

• Hardcoding tokens exposes secrets in code
• Using localStorage risks token theft via XSS
• Sending tokens in URL leaks them in logs