4xx Client Error

HTTP 401 Unauthorized

The request requires user authentication. The client must provide valid credentials (such as a token or username/password) to access the resource. Despite the name, this is about authentication, not authorization.

Common Causes

  • Missing or expired authentication token
  • Invalid API key or credentials
  • Session has timed out and user needs to re-login
  • Authorization header format is incorrect

How to Fix

  1. 1Include a valid Authorization header with your request
  2. 2Refresh expired tokens or re-authenticate
  3. 3Check that credentials are correct and not revoked
  4. 4Verify the authentication scheme (Bearer, Basic, etc.)

Example

HTTP 401 Unauthorized
GET /api/profile HTTP/1.1

→ 401 Unauthorized
→ WWW-Authenticate: Bearer realm="api"

Related Client Error Codes

400

Bad Request

402

Payment Required

403

Forbidden

404

Not Found

405

Method Not Allowed

406

Not Acceptable

407

Proxy Authentication Required

408

Request Timeout

409

Conflict

410

Gone

411

Length Required

412

Precondition Failed

413

Content Too Large

414

URI Too Long

415

Unsupported Media Type

416

Range Not Satisfiable

417

Expectation Failed

418

I'm a Teapot

421

Misdirected Request

422

Unprocessable Content

423

Locked

424

Failed Dependency

425

Too Early

426

Upgrade Required

428

Precondition Required

429

Too Many Requests

431

Request Header Fields Too Large

451

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