📝 Add new docs to override default error status codes

docs/en/docs/how-to/authentication-error-status-code.md

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+# Use Old 403 Authentication Error Status Codes { #use-old-403-authentication-error-status-codes }
+
+Before FastAPI version `0.122.0`, when the integrated security utilities returned an error to the client after a failed authentication, they used the HTTP status code `403 Forbidden`.
+
+Starting with FastAPI version `0.122.0`, they use the more appropriate HTTP status code `401 Unauthorized`, and return a sensible `WWW-Authenticate` header in the response, following the HTTP specifications, <a href="https://datatracker.ietf.org/doc/html/rfc7235#section-3.1" class="external-link" target="_blank">RFC 7235</a>, <a href="https://datatracker.ietf.org/doc/html/rfc9110#name-401-unauthorized" class="external-link" target="_blank">RFC 9110</a>.
+
+But if for some reason your clients depend on the old behavior, you can revert to it by overriding the method `make_not_authenticated_error` in your security classes.
+
+For example, you can create a subclass of `HTTPBearer` that returns a `403 Forbidden` error instead of the default `401 Unauthorized` error:
+
+{* ../../docs_src/authentication_error_status_code/tutorial001_py39.py hl[9:13] *}
+
+/// tip
+
+Notice that the function returns the exception instance, it doesn't raise it. The raising is done in the rest of the internal code.
+
+///