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HTTP_STATUS_LOGIN_TIMEOUT
The code is not registered by IANA, so clients must not treat it as a standard authentication challenge. Applications often use it to tell the browser to restart an interactive sign-in flow.
Check session lifetime, authentication cookies, load-balancer affinity, and clock or redirect handling. Preserve the response body because it can identify the application-specific session policy.
Because 440 is application-specific, confirm that the response truly comes from the expected Microsoft/IIS application before building client behavior around it. When it represents session expiry, the usual recovery is a new authenticated session followed by a safe replay of the intended operation, not repeated use of the stale session cookie.
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