A developer is trying to access the internal website of his company. When he opened a webpage, he received an error message notifying "Proxy Authentication Required". He approached the IT department…

A developer is trying to access the internal website of his company. When he opened a webpage, he received an error message notifying "Proxy Authentication Required". He approached the IT department in the company and reported the issue. The IT staff explained him that this is the HTTP error indicating that the client is unable to process the request due to lack of appropriate client's authentication proofs, or for a proxy that exists processing the requests between the clients and the server. Identify the HTTP error code corresponding to the above error message received by the employee?