Microsoft Security | Microsoft Entra | Microsoft Entra External ID
Managing external identities to enable secure access for partners, customers, and other non-employees
Microsoft Entra External ID custom URL domain: esctx cookies accumulate and cause HTTP 431 on a subdomain
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Boukhriss Ouchab, Marouane
0
Reputation points
We use a custom URL domain for our Entra External ID tenant (login.contoso.com, through Azure Front Door). Our own web page for creating passkeys runs on a subdomain, account.login.contoso.com, because WebAuthn requires it to be within the passkey's relying party ID.
The sign-in pages set cookies named esctx-<random> with Domain=.login.contoso.com, so the browser also sends them to our subdomain. Each sign-in adds a new one (about 0.8 KB), and none is removed until the browser closes. After roughly a dozen sign-ins in one session, requests to our subdomain exceed the usual 16 KB header limit and fail with HTTP 431.
Is this expected? Is there a setting that keeps these cookies host-only or expires old ones?
Microsoft Security | Microsoft Entra | Microsoft Entra External ID
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