What is the key difference between an HTTP 401 Unauthorized error and an HTTP 403 Forbidden error?

The key distinction lies in the concept of authentication versus authorization. A **401 Unauthorized** error means that the client has not provided valid authentication credentials. The server requires authentication to grant access. A **403 Forbidden** error, on the other hand, means the client is authenticated (or attempting to access a public resource), but the server explicitly denies access to the requested resource. This often implies that the client has insufficient permissions (authorization) to perform the action, even though their identity is known.