401 = Unauthorized (RFC 7235) - Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication. 401 semantically means "unauthenticated", i.e. the user does not have the necessary credentials. Note: Some sites issue HTTP 401 when an IP address is banned from the website (usually the website domain) and that specific address is refused permission to access a website.
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