401 unauthorized
HTTP 401 Unauthorized is a response status indicating that a request lacks valid authentication credentials for the requested resource.
Secure APIs
The HTTP 401 status code indicates that a request lacks valid authentication credentials.
- How it is used
- Distinguishes missing or invalid authentication from authenticated users who lack permission to perform an operation.
- How deep it goes
- Defines the status distinction and applies it in an automated endpoint test, without detailing authentication internals.
- Examples
- Tests an unauthenticated lesson request and runs it with pytest against a FastAPI service.
- What you can do after
- Diagnose/debug with it, identifying authentication failures and separating them from authorization failures in automated API tests.
ASP.NET Core in Action, 3e
A 401 Unauthorized response is an HTTP response indicating that authentication is required or has failed for the request.
- How it is used
- Uses 401 responses to signal failed API authentication and stop unauthenticated requests before endpoint execution.
- How deep it goes
- Explains challenges, API behavior, and bearer-header mistakes, but defers detailed authorization requirements and failure logging.
- Examples
- Uses a protected Edit action and an Authorization: Bearer <token> request to demonstrate successful correction of a 401.
- What you can do after
- Diagnose 401 responses by checking the bearer scheme, spacing, spelling, and token value before retrying an API request.
Read how ASP.NET Core in Action, 3e explains 401 unauthorized →
Related concepts
- 403 Forbiddencontrasts with · 403 Forbidden is an HTTP response status indicating that the server understood a request but refuses to authorize the requested access or operation.
- authentication errorproduced by · An authentication error is a failure to verify the identity represented by credentials submitted for access to a service or resource.
- api callproduced by · An API call is a programmatic request or invocation through an application programming interface to access data or invoke an operation.
- HTTP response codekind of · An HTTP status code is a standardized three-digit value in an HTTP response that indicates the outcome of processing the corresponding request.
- authenticationproduced by · Authentication is the process of establishing or verifying the identity of a user, service, device, or other communicating entity.
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