Token-based authentication in Ruby on Rails - Mini Project: Build & Apply

Token-based authentication

📖 Scenario: You are building a simple Rails API that uses token-based authentication to secure user access. Users will have unique tokens that the server checks to allow or deny access to protected resources.

🎯 Goal: Create a Rails controller that authenticates users by checking a token sent in the request headers. You will set up a user data structure, configure a token variable, implement the authentication logic, and complete the controller to respond based on token validity.

📋 What You'll Learn

Create a hash called USERS with usernames as keys and tokens as values

Add a variable valid_token to hold the token from request headers

Write a method authenticate_user that checks if valid_token matches any token in USERS

Complete the controller action to render json: { message: 'Access granted' } if authenticated, else json: { message: 'Access denied' }

💡 Why This Matters

🌍 Real World

Token-based authentication is commonly used in APIs to secure access without sessions or cookies. It allows stateless, scalable authentication.

💼 Career

Understanding token-based authentication is essential for backend developers building secure APIs and services.

1

Set up user tokens

Create a constant hash called USERS with these exact entries: 'alice' => 'token123', 'bob' => 'token456', and 'carol' => 'token789'.

Ruby on Rails

# Create USERS hash with usernames and tokens
# Your code here

Hint

Use a Ruby hash with string keys and string values for tokens.

2

Get token from request headers

Add a variable called valid_token that gets the token from request.headers['Authorization'] inside the controller action.

Ruby on Rails

USERS = {
  'alice' => 'token123',
  'bob' => 'token456',
  'carol' => 'token789'
}

class ApiController < ApplicationController
  def authenticate
    # Get token from headers
    # Your code here
  end
end

Hint

Use request.headers['Authorization'] to get the token string.

3

Check token validity

Inside the authenticate method, write a condition that sets authenticated to true if valid_token is included in the values of USERS, otherwise false.

Ruby on Rails

USERS = {
  'alice' => 'token123',
  'bob' => 'token456',
  'carol' => 'token789'
}

class ApiController < ApplicationController
  def authenticate
    valid_token = request.headers['Authorization']
    # Check if token is valid
    # Your code here
  end
end

Hint

Use USERS.value?(valid_token) to check if the token exists.

4

Respond based on authentication

Complete the authenticate method to render json: { message: 'Access granted' } if authenticated is true, else render json: { message: 'Access denied' }.

Ruby on Rails

USERS = {
  'alice' => 'token123',
  'bob' => 'token456',
  'carol' => 'token789'
}

class ApiController < ApplicationController
  def authenticate
    valid_token = request.headers['Authorization']
    authenticated = USERS.value?(valid_token)
    # Render JSON response based on authentication
    # Your code here
  end
end

Hint

Use an if statement to render different JSON messages based on authenticated.

Practice

1. What is the main purpose of token-based authentication in Rails?

easy

A. To identify users securely without requiring passwords every time

B. To store user passwords in plain text

C. To create server sessions for each user

D. To encrypt database records automatically

Solution

1. Step 1: Understand token-based authentication

   Token-based authentication uses a secret token to identify users securely without needing passwords repeatedly.

2. Step 2: Compare options

   Only To identify users securely without requiring passwords every time correctly describes this purpose; others describe unrelated or incorrect behaviors.

3. Final Answer:

   To identify users securely without requiring passwords every time -> Option A

4. Quick Check:

   Token-based authentication = Identify users securely without passwords [OK]

Hint: Tokens replace passwords for repeated user identification [OK]

Common Mistakes:

• Confusing tokens with password storage
• Thinking tokens create server sessions
• Assuming tokens encrypt data automatically

2. Which Rails method adds a secure token to a model for token-based authentication?

easy

A. has_secure_password

B. validates_token

C. has_secure_token

D. generate_token

Solution

1. Step 1: Recall Rails token helper methods

   Rails provides has_secure_token to add a secure token to models easily.

2. Step 2: Eliminate incorrect options

   has_secure_password is for passwords, not tokens; others are not valid Rails methods.

3. Final Answer:

   has_secure_token -> Option C

4. Quick Check:

   Token method in Rails = has_secure_token [OK]

Hint: Remember: token method is 'has_secure_token' not 'password' [OK]

Common Mistakes:

• Confusing has_secure_token with has_secure_password
• Using non-existent methods like generate_token
• Assuming validates_token is built-in

3. Given the model code:

class User < ApplicationRecord
  has_secure_token :auth_token
end

user = User.new
user.save
puts user.auth_token.nil?

What will be the output?

medium

A. false

B. Error: undefined method

C. nil

D. true

Solution

1. Step 1: Understand has_secure_token behavior

   When a new User is saved, Rails automatically generates a unique token for auth_token, so it won't be nil.

2. Step 2: Evaluate the output of puts user.auth_token.nil?

   Since auth_token is set, nil? returns false, so output is false.

3. Final Answer:

   false -> Option A

4. Quick Check:

   Token generated on save = false for nil? [OK]

Hint: Tokens auto-generate on save, so nil? returns false [OK]

Common Mistakes:

• Assuming token is nil before save
• Expecting nil output instead of false
• Confusing method names causing errors

4. Identify the error in this token authentication setup:

class ApiUser < ApplicationRecord
  has_secure_token :auth_token
end

user = ApiUser.new
user.auth_token = nil
user.save
puts user.auth_token.nil?

medium

A. user.save will raise an exception due to nil token

B. has_secure_token requires a token column named 'token', not 'auth_token'

C. Token is not generated because auth_token was manually set to nil before save

D. No error; output will be false

Solution

1. Step 1: Recall has_secure_token generation condition

   has_secure_token :auth_token generates a token if auth_token.blank? before save (nil.blank? returns true).

2. Step 2: Trace code execution

   Setting user.auth_token = nil keeps it blank, so save generates the token. user.auth_token.nil? returns false. No error.

3. Final Answer:

   No error; output will be false -> Option D

4. Quick Check:

   nil.blank? = true -> generates token [OK]

Hint: Setting to nil does NOT prevent generation; nil.blank? = true [OK]

Common Mistakes:

• Thinking setting to nil prevents token generation
• Expecting save to raise error on nil token
• Thinking output is true because manually set to nil

5. You want to secure an API in Rails using token-based authentication. Which approach correctly checks the token sent in request headers against the stored user token?

hard

A. Store tokens in cookies and check them with session[:token]

B. Use before_action to find user by auth_token from request.headers['Authorization'] and reject if not found

C. Use has_secure_password to verify token in params

D. Generate a new token on every request and compare with stored token

Solution

1. Step 1: Understand token authentication in APIs

   APIs commonly send tokens in headers; Rails can check request.headers['Authorization'] to find the user.

2. Step 2: Evaluate options for correctness

   Use before_action to find user by auth_token from request.headers['Authorization'] and reject if not found correctly uses before_action to authenticate by token. Options B and C misuse cookies and password helpers. Generate a new token on every request and compare with stored token is insecure and impractical.

3. Final Answer:

   Use before_action to find user by auth_token from request.headers['Authorization'] and reject if not found -> Option B

4. Quick Check:

   API token check = before_action with header token [OK]

Hint: Check token in headers with before_action for API security [OK]

Common Mistakes:

• Using cookies or sessions for API token storage
• Confusing password helpers with token verification
• Generating new token each request causing mismatch