What is authentication and authorization?

Authentication and authorization are two fundamental security concepts in application development. While they work together to secure applications, they serve different purposes and are often misunderstood or conflated.

What is authentication?

Authentication answers the question “Who are you?” It’s the process of confirming a user’s identity through some form of verification. This is different from authorization, which answers “What are you allowed to do?” and determines what resources or actions a user can access.

As a real-world example, let’s say you’re trying to enter a secure building. You show your ID to the security guard, and they agree that ID matches who you are — this is authentication.

What is authorization?

Authorization is the process of determining what an authenticated user is allowed to do. It happens after authentication and involves checking permissions, roles, or policies to decide whether to grant or deny access to specific resources or actions.

Continuing the building example, even after the security guard verifies your identity (authentication), they still need to check if you’re authorized to enter that particular building. They might consult a list of authorized personnel or check your access level.

Common authorization patterns

Role-based access control (RBAC)

Users are assigned roles, and roles have permissions. For example:

• Admin role: Can create, read, update, and delete all resources
• Editor role: Can read and update content, but not delete
• Viewer role: Can only read content

Attribute-based access control (ABAC)

Access decisions are based on attributes of the user, resource, environment, or action. For example:

• Users can only edit documents they created
• Access is restricted during business hours
• Users can only view sensitive data if they’re in the office

Policy-based authorization

Access decisions are made based on defined policies that can consider multiple factors:

• “Users can access financial data only if they have completed security training”
• “Managers can approve expenses up to $10,000”
• “External users can only access public resources”

The relationship between authentication and authorization

Authentication and authorization work together in a sequence:

1. Authentication first: Verify who the user is
2. Authorization second: Determine what they can do

You can’t authorize someone without first knowing who they are, but authentication alone doesn’t grant any access. Both are essential for secure applications.

Real-world examples

Banking application:

• Authentication: User logs in with username and password
• Authorization: User can view their own accounts but not others’

Content management system:

• Authentication: Editor logs in with credentials
• Authorization: Editor can modify articles but not delete the entire site

API access:

• Authentication: Application authenticates with API key
• Authorization: API key has specific scopes (read-only vs. read-write)

Why authentication and authorization matter

Every application that handles user data or provides personalized experiences needs both authentication and authorization. Without them, you can’t:

Security

• Protect user data from unauthorized access
• Prevent privilege escalation attacks
• Ensure users only access what they’re supposed to

User experience

• Provide personalized experiences based on user roles
• Show relevant content and features
• Maintain user sessions securely

Compliance and governance

• Meet regulatory requirements for data protection
• Implement audit trails for access decisions
• Enforce organizational policies

Business logic

• Implement different pricing tiers
• Control feature access based on subscription levels
• Manage multi-tenant applications

Common challenges

Building authentication and authorization systems presents several challenges:

Security complexity

Both systems are prime targets for attackers. You need to handle:

• Secure password storage and verification
• Session management and token security
• Protection against common attacks (brute force, session hijacking, privilege escalation)
• Proper permission checking at every access point

User experience

Security measures can’t come at the expense of usability:

• Users expect smooth, fast authentication flows
• Authorization should be transparent when possible
• Error messages should be helpful without revealing sensitive information

Standards and compatibility

Different platforms and services use different protocols:

• Integrating with multiple systems requires understanding various standards
• OAuth, SAML, and other protocols have their own complexities
• Maintaining compatibility across different client types

Maintenance and updates

Security threats evolve constantly:

• Authentication and authorization systems need regular updates
• Security patches and monitoring are essential
• Policies and permissions need ongoing management

Understanding these concepts helps you design systems that are both secure and user-friendly, while meeting your application’s specific requirements for access control.