AuthN vs AuthZ: The Differences You Need to Know [2025]

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Introduction

If you’ve ever checked into a hotel, you’ve already experienced the difference between authentication (AuthN) and authorization (AuthZ). When you show your ID at the front desk, you’re proving who you are—that’s authentication. Once your identity is confirmed, the hotel decides what you can access: which room you get a key for, whether you can use the pool, gym, or member lounges. That’s authorization.

AuthN and AuthZ sound similar, and sometimes people use them interchangeably, but they actually solve two very different problems in your codebase. AuthN confirms your identity, while AuthZ determines what actions and resources you can access based on factors like your role or team. Understanding the difference is essential for building secure systems and making sure users only get access to what they’re allowed.

TL;DR

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AuthN confirms identity, while AuthZ controls access based on that identity. Both are essential for secure applications.

Core Differences

AuthN and AuthZ might seem like two sides of the same coin, and it’s easy to see why people mix them up, but they actually solve very different problems in your application.

AuthN is about identity. Imagine someone trying to check into a hotel. The front desk asks for their ID to confirm they really are who they claim to be. If the ID doesn’t match, they’re politely turned away—no room key, no access. This is AuthN: the process that confirms a user’s identity before anything else happens.

AuthZ is about access and privileges. Once AuthN is successful, the hotel staff checks the reservation details. Maybe the guest has a standard room, or maybe their membership status or special package gives them access to free breakfast, a member lounge, or even a welcome gift. This is AuthZ: where your application determines what resources or actions a user is allowed, based on their role, status, or permissions.

In short:

• AuthN: Are you really who you say you are? If not, you don’t get in.
• AuthZ: Now that we know who you are, what are you allowed to do? Your status or package decides.

These two processes work together to protect identity and control access to resources, ensuring users only get what they’re supposed to—no more, no less.

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Common Types

Understanding how AuthN and AuthZ are implemented in real-world applications helps clarify their roles, the tools you might use for each, and the different authentication and authorization types available.

AuthN Types:

• Passwords: Still the most common approach, though not always the most secure.
• Multi-factor authentication (MFA): Adds an extra layer by requiring something you know (like a password) plus something you have (like a code from your phone).
• Biometrics: Uses fingerprints, facial recognition, or voice to confirm identity.
• Single sign-on (SSO): Lets users authenticate once and access multiple systems without logging in again.
• OAuth/OpenID Connect: Protocols that let users log in using credentials from another trusted provider.

AuthZ Types:

• Role-based access control (RBAC): Grants permissions based on a user’s role (admin, editor, viewer, etc.).
• Attribute-based access control (ABAC): Makes decisions based on attributes like department, location, or time of access.
• Relationship-Based Access Control (ReBAC): Permissions depend on the relationships between users and resources.
• Access control lists (ACLs): Define specific permissions for users or groups on particular resources.
• Custom policies: Many apps use their own logic or rules to determine what users can do, often combining elements of RBAC and ABAC.

Both AuthN and AuthZ are essential for secure access control, and understanding the available types helps you choose the right approach for your application’s needs.

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Why It Matters

Getting AuthN and AuthZ right is fundamental for protecting your users and your data. When these two processes work together, only verified users can access your application, and each user is limited to the permissions they are supposed to have.

If AuthN is weak, anyone could pretend to be someone else and gain access. If AuthZ is not set up correctly, even a legitimate user might see sensitive resources they should not, or get blocked from features they actually need. This can lead to data breaches, compliance problems, and a frustrating user experience.

For developers, understanding the difference between AuthN and AuthZ makes it easier to design secure systems, troubleshoot access issues, and scale your application as your user base grows. Strong AuthN and AuthZ are essential for building trust and keeping your application safe.

Enough about hotels—let’s look at how authentication and authorization actually play out in a real software application.

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Real-World Use Case: Project Management App

Imagine you’re building a project management tool like Trello or Jira. Here’s how AuthN and AuthZ come into play: 

AuthN: When a user logs in with their email and password (or via Google SSO), the app verifies their identity. This step ensures the user is who they claim to be.

AuthZ: Once authenticated, the app checks what the user is allowed to do—like viewing boards, creating tasks, or managing team members—based on their role.

To visualize this, here’s an Access Matrix Table showing which roles have which permissions:

This table makes it easy to see at a glance which roles can do what, clarifying how authorization decisions are made in your app. For more complex scenarios, like relationship-based access control (ReBAC), you could extend this table or add notes to represent permissions based on user-resource relationships.

Oso’s Perspective

For most teams, authentication is pretty straightforward—just plug into an identity provider or use a standard library and you’re set. Authorization, on the other hand, is where things get complicated. Here are some common pain points developers run into with AuthZ:

• Scattered permission checks: As your app grows, access control logic often ends up spread across controllers, services, and middleware, making it hard to see the big picture or audit who can do what.
• Changing requirements: Business rules evolve. Suddenly, you need to support new roles, special cases, or complex hierarchies, and updating your authorization logic everywhere becomes a headache.
• Lack of consistency: When authorization is handled in multiple places, it’s easy to miss something and accidentally grant (or deny) access where you shouldn’t.
• Testing and debugging: Tracking down why a user does or doesn’t have access to a resource can be tricky when the logic is scattered and hard to follow.

Oso provides Authorization as a service and solves these headaches by giving you a centralized, declarative way to define your authorization policies in code. With Oso, you can:

• Centralize your access control logic so it’s easy to review and update.
• Define roles, permissions, and custom rules in a clear, maintainable way.
• Adapt quickly as your requirements change, without hunting down permission checks scattered throughout your codebase.
• Debug and audit your authorization decisions with confidence, since everything is in one place.
• Test your policies to ensure your authorization logic works as expected before it hits production.

By taking the complexity out of AuthZ, Oso lets you focus on building features, not fighting with permissions.

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FAQs/Common Confusions

What’s the difference between AuthN and AuthZ, really?
AuthN (authentication) is about confirming a user’s identity—proving they are who they say they are. AuthZ (authorization) is about determining what actions or resources that user can access, often based on their role or permissions.

Can you have AuthZ without AuthN?
No. Authorization decisions depend on knowing who the user is. Without authentication, there’s no way to know which permissions to check.

Why do people mix up AuthN and AuthZ?
The terms sound similar and both deal with access control, but they solve different problems. AuthN answers “Who are you?” AuthZ answers “What are you allowed to do?”.

Is OAuth authentication or authorization?
OAuth is a way of establishing identity using a token, but it’s often used alongside authorization. Once you have a token that establishes your identity, you can also include data on that token that can be used for authorization. OAuth manages confirming identity and managing the token.

What are some common mistakes with AuthN and AuthZ?

• Treating authentication as enough and forgetting to check authorization.
• Scattering permission checks throughout the codebase, making it hard to audit or update.
• Not updating authorization rules as business requirements change.

Are there best practices for implementing AuthN and AuthZ?
Yes. Use established libraries or providers for authentication, and centralize your authorization logic for easier maintenance and auditing. Always keep them as separate concerns in your architecture.

If you’re ever unsure, just remember: AuthN is “Who are you?” AuthZ is “What can you do?”

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Conclusion

Understanding the difference between AuthN and AuthZ is essential for building secure and reliable applications. AuthN (authentication) confirms a user’s identity, while AuthZ (authorization) determines what actions and resources that user can access, often based on their role or other factors. Both are crucial parts of access control and work together to protect your users and your data.

As your application grows, keeping authentication and authorization concerns separate—and using the right tools for each—will help you maintain security, simplify your codebase, and adapt to changing requirements. Whether you’re just starting out or scaling up, investing in strong AuthN and AuthZ practices will pay off in the long run. If you'd like to discuss building those practices into your application, reach out to us on slack.