Authentication checks that you are signed in as the account you claim; authorization checks whether that account is allowed to do what you requested. A successful sign-in does not grant every permission: you might be able to open a project but still be blocked from deleting someone else’s repository.
What authentication and authorization mean
Authentication establishes that a claimant controls one or more authenticators associated with an account or digital identity. In plain language, it answers “Who are you?”—more precisely, whether the evidence used to claim an identity is valid. NIST defines authentication in SP 800-63B-4.
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Authorization is the decision about whether a subject may access a resource or perform an action. It answers “What can you do?” NIST defines it as “A decision to grant access, typically automated by evaluating a subject’s attributes” in SP 800-63-4.
The shorthand questions are useful, but they are not complete technical definitions. Authentication evaluates evidence tied to an account; authorization evaluates a request against access rules. Depending on the system, those rules can account for attributes such as the subject, resource, or requested action.
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How the two decisions differ
| Question | Authentication | Authorization |
|---|---|---|
| What does it answer? | Is the claimant in control of authenticators associated with the claimed account? | May this subject access this resource or perform this action? |
| What is evaluated? | Account-associated authenticators, such as credentials used to sign in. | Whether access should be granted, often by evaluating subject attributes. |
| What is the result? | An authentication result or event that can establish an authenticated session. | An allow-or-deny decision for a particular resource or action. |
| Example | A user signs in and the system verifies the account-associated credentials. | The signed-in user can view a project but lacks permission to delete it. |
The table describes the concepts, not a required architecture. Applications can arrange checks differently, but proving an account claim and deciding access are distinct questions.
Why signing in does not mean unlimited access
After authentication, a service may recognize the account and still restrict what it can do. For example, a repository service can let a user sign in and view a project while denying a request to delete a repository they do not own or administer. Authentication establishes the relevant identity; the authorization rule determines whether that specific action is permitted.
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This distinction also helps diagnose access problems. If sign-in fails, the issue concerns the authentication attempt or its evidence. If sign-in succeeds but one feature or resource is unavailable, the cause may be an authorization rule, role, or permission—not necessarily a failure to identify the user.
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OAuth 2.0 and OpenID Connect are not interchangeable
OAuth 2.0 delegates access
RFC 6749 defines OAuth 2.0 as an authorization framework that lets an application obtain limited access to a protected HTTP service, including delegated access on a resource owner’s behalf. An OAuth access token is used to authorize access to a protected resource; by itself, it is not standardized proof of a user’s identity.
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OpenID Connect adds identity information
OpenID Connect adds an identity layer to OAuth-based flows. NIST’s federation guidance in SP 800-63C-4 describes an ID Token as a signed assertion carrying information about the subscriber and authentication event. That is different in purpose from an OAuth access token, which can protect an API such as the UserInfo endpoint. Do not treat the two tokens as interchangeable: one conveys identity and authentication information, while the other authorizes access to a protected resource.
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NIST’s SP 800-63-4, Digital Identity Guidelines, published in July 2025, supersedes SP 800-63-3. Its scope covers identity proofing, authentication, and federation for people interacting with government information systems over networks. It is useful guidance, but its requirements do not automatically govern every private application.
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RFC 6749 is an IETF Standards Track document dated October 2012. The RFC Editor notes that it has subsequent updates. It defines OAuth 2.0’s framework, but implementation guidance should account for the current RFC series rather than relying on the original document alone.
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