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HLDsystem_design~12 mins

Authentication vs authorization in HLD - Architecture Patterns Compared

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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
Test your understanding
Which component verifies the user's identity?
AAPI Gateway
BResource Service
CAuth Service
DLoad 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.