Authentication vs Authorization

Authentication and authorization are two distinct security processes: authentication verifies who a user is, while authorization decides what that user is allowed to access. Authentication checks a claimed identity against stored factors, and authorization checks the confirmed identity against an access policy. The National Institute of Standards and Technology (NIST) defines both as separate controls in its access control and identity guidance.

This article defines authentication and authorization, explains how they differ, sets out the order in which they run, describes how they work together, gives examples of login followed by permissions, and identifies the protocols that implement each. A comparison table summarizes the differences.

Each section states one part of the topic and connects it to the separation between verifying identity and granting access at the center of the definition. The result is a complete account of how authentication and authorization differ and how the two combine to control access to a system.

What Is the Difference Between Authentication and Authorization?

Authentication is the process of verifying who a user is, while authorization is the process of deciding what that verified user is allowed to access. Authentication confirms identity, and authorization assigns permissions to the confirmed identity. The defining differences are listed below:

• Authentication verifies identity by checking factors such as a password, a key, or a fingerprint.
• Authorization grants access rights by checking a verified identity against an access policy.
• Authentication answers the question of who the user is before any resource is reached.
• Authorization answers the question of what the user may do once identity is confirmed.

Authentication confirms identity, the process defined in the explanation of what authentication is, while authorization enforces the permissions that access control models define. The two processes appear together but serve separate purposes.

What Is Authentication?

Authentication is the process of verifying that a user, device, or system is who or what it claims to be by checking one or more factors. Authentication tests submitted credentials against stored records to confirm a claimed identity. The traits of authentication are listed below:

• Identity claim presents a username or account that the user asserts as their own.
• Factor verification checks a password, a security key, or a biometric trait against stored data.
• Confirmation establishes a verified session when the factors match the stored credentials.
• Multi-factor option requires two or more independent factors to strengthen the verification.

Authentication establishes the verified identity that every later decision depends on, the factors and methods detailed in the guide to authentication. Requiring more than one factor in this step follows the approach of multi-factor authentication.

What Is Authorization?

Authorization is the process of granting a verified identity the specific permissions and access rights its role requires. Authorization runs after authentication, applying an access policy to decide which resources and actions the confirmed identity may use. The traits of authorization are listed below:

• Permission assignment grants a verified identity rights over specific resources and actions.
• Policy evaluation checks the identity against rules such as roles, attributes, or access lists.
• Least privilege limits each identity to the minimum access its role requires.
• Enforcement blocks any action that the access policy does not permit for the identity.

Authorization assigns and enforces the permissions that follow a confirmed identity, the rules that access control models such as role-based access control define. A policy that grants minimum access supports the least-privilege principle in zero trust security.

What Is the Order of Authentication and Authorization?

Authentication always runs before authorization, because a system must confirm an identity before it can decide what that identity is allowed to access. The order is fixed, since authorization has no identity to evaluate until authentication completes. The sequence is listed below:

1. Authentication verifies the claimed identity by checking the submitted factors.
2. Session establishment issues a verified session or token for the confirmed identity.
3. Authorization evaluates the confirmed identity against the access policy for each request.
4. Access decision grants or denies the requested resource based on the policy result.

Authentication precedes authorization in every access flow, since a permission decision requires a confirmed identity, according to NIST access control guidance. A request that fails authentication never reaches the authorization step.

How Do Authentication and Authorization Work Together?

Authentication and authorization work together by confirming an identity first and then applying that identity’s permissions to every request. The two processes form one access control flow, where the verified identity from authentication feeds the policy decision in authorization. The combined flow is listed below:

• Verified identity from authentication becomes the input that authorization evaluates.
• Token or session carries the confirmed identity so authorization runs without rechecking factors.
• Per-request checks let authorization decide access for each resource a session requests.
• Combined enforcement blocks an attempt that fails either the identity check or the permission check.

Authentication and authorization combine into the access control flow that protects a system, the models detailed in the guide to access control. A single sign-on system authenticates once and authorizes across many applications, the design behind single sign-on.

What Are Examples of Authentication and Authorization?

An example of authentication is logging in with a password and a one-time code, and an example of authorization is the set of permissions that login grants inside the application. The two appear in sequence in everyday access. The examples are listed below:

• Login authentication verifies a user with a password and a one-time code at sign-in.
• Role authorization grants an administrator more permissions than a standard user after login.
• File authorization allows one identity to read a file while another may edit or delete it.
• API authorization issues a token that limits an application to specific actions on a user’s behalf.

A login confirms identity through authentication, and the permissions inside the application come from authorization. The single login that grants access across many services illustrates the design of single sign-on, where one authentication event drives many authorization decisions.

Authentication vs Authorization Comparison Table

What Protocols Handle Authentication and Authorization?

OpenID Connect and SAML handle authentication, while OAuth 2.0 handles authorization, each standardizing how identity and access pass between systems. A protocol defines the messages and tokens that carry identity or permission. The relevant protocols are listed below:

• OAuth 2.0 handles authorization, issuing access tokens that grant an application limited rights on a user’s behalf.
• OpenID Connect (OIDC) handles authentication, adding an identity layer on top of OAuth 2.0 to verify users.
• Security Assertion Markup Language (SAML) handles authentication, exchanging identity assertions between an identity provider and a service.
• Tokens carry the result, with identity tokens for authentication and access tokens for authorization.

OAuth 2.0 grants permissions without sharing a password, while OpenID Connect and SAML verify identity, according to the specifications published by the OpenID Foundation and OASIS. These protocols often support single sign-on, letting one identity provider authenticate a user for many services.

What Are the Models of Authorization?

The models of authorization are role-based, attribute-based, and discretionary access control, each deciding permissions through a different rule set. An authorization model defines how a system maps a verified identity to access rights. The models of authorization are listed below:

• Role-based access control (RBAC) grants permissions through roles assigned to each verified identity.
• Attribute-based access control (ABAC) grants permissions by evaluating attributes such as department, device, and time.
• Discretionary access control (DAC) lets a resource owner decide which identities receive access.
• Mandatory access control (MAC) enforces permissions through system-wide policy labels rather than owner choice.

Role-based access control assigns permissions by role, while attribute-based access control evaluates context, the models detailed in the guide to access control. Each model acts only after authentication confirms the identity it evaluates.

What Are Common Misconceptions About Authentication and Authorization?

A common misconception is that authentication and authorization are the same process, when in fact authentication verifies identity and authorization grants permissions. Confusing the two leads to gaps in access control. The common misconceptions are listed below:

• Treating them as one step ignores that a verified identity still needs a separate permission check.
• Assuming login grants full access overlooks that authorization limits a verified user to specific resources.
• Using OAuth for identity misapplies an authorization protocol where OpenID Connect verifies identity.
• Skipping least privilege grants a verified user more access than the role requires.

Authentication and authorization remain separate even when one screen handles both, the distinction reinforced by the guide to access control. A least-privilege policy limits a verified identity to its required access, a core principle of zero trust security.

Where Are Authentication and Authorization Used Together?

Authentication and authorization are used together in web applications, operating systems, APIs, and networks, wherever a system controls access to resources. The pair appears in any access flow. The common settings are listed below:

• Web applications authenticate a user at login and authorize each action against the user’s role.
• Operating systems authenticate an account and authorize file and system access by permissions.
• APIs authenticate a client and authorize each request through scoped access tokens.
• Networks authenticate a device and authorize its reach through access control lists.

Every protected system pairs an identity check with a permission check, the access control flow detailed in the guide to access control. A single sign-on system centralizes the authentication step across many applications, the design behind single sign-on.

Key Takeaways

• Authentication verifies who a user is, while authorization decides what the user may access.
• Authentication checks factors, while authorization checks an identity against a policy.
• Order places authentication first, since authorization needs a confirmed identity.
• Together they form the access control flow that protects a system.
• Protocols use OpenID Connect and SAML for authentication and OAuth 2.0 for authorization.
• Examples pair a login with the permissions that login grants inside an application.

Last Thoughts on Authentication vs Authorization

Authentication and authorization are distinct processes: authentication verifies who a user is, while authorization decides what that verified user is allowed to access. Authentication checks factors against credentials and runs first, and authorization checks the confirmed identity against an access policy.

The two combine into one access control flow, where OpenID Connect and SAML verify identity and OAuth 2.0 grants permissions. Readers can continue with the explanation of what authentication is, the guide to access control, the overview of single sign-on, or the overview of cybersecurity.