Authentication vs authorization in HLD - Architecture Patterns Compared

System Overview - Authentication vs authorization

This system explains the difference between authentication and authorization in a typical web application. Authentication verifies who the user is, while authorization determines what the user can do. The system ensures secure access by checking identity first, then permissions.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +-------------------+
  |                   |
  v                   v
Auth Service       Resource Service
  |                   |
  v                   v
User Database      Permissions Database
  |
  v
Cache (for sessions and tokens)

Components

User

client

Person or system trying to access resources

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Entry point that routes requests to authentication or resource services

Auth Service

service

Handles user identity verification (authentication)

Resource Service

service

Handles user permissions and resource access (authorization)

User Database

database

Stores user credentials and profile data for authentication

Permissions Database

database

Stores user roles and permissions for authorization

Cache

cache

Stores session tokens and permission data for faster access

Request Flow - 14 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Auth Service

Auth Service → User Database

User Database → Auth Service

Auth Service → Cache

API Gateway → Resource Service

Resource Service → Cache

Resource Service → Permissions Database

Permissions Database → Resource Service

Resource Service → Cache

Resource Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Auth Service

Impact:Users cannot log in or verify identity, blocking access to resources

Mitigation:Use multiple Auth Service instances with load balancing and failover; cache valid session tokens to allow continued access for logged-in users

Architecture Quiz - 3 Questions

Which component verifies the user's identity?

A API Gateway

B Resource Service

C Auth Service

D Load Balancer

Design Principle

This architecture clearly separates authentication (identity verification) from authorization (permission checking), improving security and scalability by using dedicated services and caching to optimize performance.

Practice

1. Which of the following best describes authentication in system design?

easy

A. Encrypting user data

B. Granting access to resources

C. Logging user activities

D. Verifying the identity of a user

Solution

1. Step 1: Understand authentication purpose

   Authentication is the process of confirming who the user is by checking credentials like username and password.

2. Step 2: Differentiate from authorization

   Authorization controls what the user can do after identity is confirmed, not the identity check itself.

3. Final Answer:

   Verifying the identity of a user -> Option D

4. Quick Check:

   Authentication = Verifying identity [OK]

Hint: Authentication = Who you are, Authorization = What you can do [OK]

Common Mistakes:

• Confusing authentication with authorization
• Thinking authentication controls permissions
• Mixing identity verification with data encryption

2. Which of the following is a correct example of an authorization check in code?

easy

A. if user.password == input_password:

B. if user.session_token is not None:

C. if user.role == 'admin':

D. if user.email_verified:

Solution

1. Step 1: Identify authorization logic

   Authorization checks what actions a user can perform, often by checking roles or permissions like user.role == 'admin'.

2. Step 2: Differentiate from authentication checks

   Authentication checks credentials like passwords or tokens, not roles.

3. Final Answer:

   if user.role == 'admin': -> Option C

4. Quick Check:

   Authorization checks roles/permissions [OK]

Hint: Authorization checks roles or permissions, not passwords [OK]

Common Mistakes:

• Using password checks as authorization
• Confusing session token presence with authorization
• Checking email verification as authorization

3. Consider this code snippet:

def access_resource(user):
    if not user.is_authenticated:
        return "Access Denied"
    if user.permission != 'read':
        return "Permission Denied"
    return "Resource Content"

What will be the output if user.is_authenticated is True but user.permission is 'write'?

medium

A. "Permission Denied"

B. "Resource Content"

C. "Access Denied"

D. Error due to missing permission

Solution

1. Step 1: Check authentication condition

   The user is authenticated (True), so the first if condition fails and does not return "Access Denied".

2. Step 2: Check authorization condition

   The user's permission is 'write', which is not equal to 'read', so the second if returns "Permission Denied".

3. Final Answer:

   "Permission Denied" -> Option A

4. Quick Check:

   Authenticated but wrong permission = Permission Denied [OK]

Hint: Authenticated? Check permission next for authorization [OK]

Common Mistakes:

• Ignoring permission check and returning resource
• Confusing authentication failure with permission failure
• Assuming 'write' permission equals 'read'

4. A developer wrote this code to check access:

if user.is_authorized:
    print("Access granted")
else:
    print("Access denied")

But the system always denies access even for valid users. What is the likely issue?

medium

A. The variable is_authorized is misspelled

B. The code checks authorization without authenticating the user first

C. The print statements are reversed

D. The user object is not defined

Solution

1. Step 1: Analyze authentication and authorization order

   Authorization should only be checked after confirming the user is authenticated. Skipping authentication can cause authorization to fail.

2. Step 2: Understand why access is always denied

   If is_authorized depends on authentication, but authentication is missing, it will always be false or unset, denying access.

3. Final Answer:

   The code checks authorization without authenticating the user first -> Option B

4. Quick Check:

   Authenticate before authorizing [OK]

Hint: Always authenticate before authorization checks [OK]

Common Mistakes:

• Checking authorization without authentication
• Assuming authorization implies authentication
• Ignoring user object initialization

5. In designing a secure web service, which approach correctly applies authentication and authorization to protect user data?

hard

A. Authenticate users with passwords, then authorize access based on roles before serving data

B. Authorize users first, then authenticate them before data access

C. Allow data access after authentication without any authorization checks

D. Skip authentication if the user has a valid session token

Solution

1. Step 1: Understand correct security flow

   First, confirm user identity by authentication (e.g., passwords). Then, check what the user is allowed to do by authorization (e.g., roles).

2. Step 2: Evaluate options for security best practice

   Authenticate users with passwords, then authorize access based on roles before serving data follows the correct order: authenticate then authorize. Other options either reverse order, skip authorization, or skip authentication improperly.

3. Final Answer:

   Authenticate users with passwords, then authorize access based on roles before serving data -> Option A

4. Quick Check:

   Authenticate first, then authorize [OK]

Hint: Authenticate identity first, then authorize actions [OK]

Common Mistakes:

• Reversing authentication and authorization order
• Skipping authorization after authentication
• Trusting session tokens without authentication