Structured Incident Report — Passthrough Token Validation Failure (Azure Portal / MSAL)

Question

Structured Incident Report — Passthrough Token Validation Failure (Azure Portal / MSAL)

H4d0 0

Dear Team,

Please be aware:

Date: 19 September 2026

Location: Romania

System: Azure Portal (Version 18.248.0.1)

Session IDs Observed:

a62bb19736fb4c4aa0fe537017ed681d

Aa34a3a1864f4cf8ae08964194ac0c36

Hey Lalima, Azure Portal failed to validate authentication tokens during resource provider calls. The portal attempted to use passthrough tokens lacking required resource provider (RP) context, resulting in repeated 401 Invalid Token responses.

This is an admin prank? The failure is reproducible across sessions and timestamps.

Evidence Extracted From Logs

2.1 Key Error Messages

From the uploaded logs:

“Token validation failed. A passthrough token was detected without proper resource provider context” “error="invalid_token", error_description="Passthrough token detected but secure validation specified at resource provider context."”

These lines appear in both incidents (09:44 and 09:52), confirming a persistent issue.

HTTP Response Details

Status: 401 Unauthorized

Error Code: PassthroughTokenValidationFailed

Failure Cause: gateway

Correlation IDs:

3b40673c-183e-4e23-a398-caedae707de5
7a480065-bf67-49a4-b054-e870e8170d6e

Portal Modules Involved

msal-browser-1p-v513.js

MsPortalFx.Base.Diagnostics.ErrorReporter

KavaJfv2fdrz.js

1i5xRkbowapb.js

These modules handle token acquisition, validation, and RP communication.

Technical Root Cause

The Azure Portal attempted to forward a passthrough token to backend resource providers (ARM, RBAC, Storage, Compute). The token did not contain the required RP context, causing the backend to reject it.

Based on the logs and typical MSAL behavior, the failure is caused by one or more of the following:

Stale or corrupted MSAL tokens

Tenant issuing legacy ARM tokens (common in system tenants)

Missing or misconfigured resource provider registrations

Conditional Access or token lifetime policies interfering

Cross‑tenant contamination (logging into multiple directories)

Portal unable to acquire a modern ARM token for this tenant

Could you please investigate and advise?

Kind Regards,

H4d0

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1 answer

Your answer

Answer 1

Hi @H4d0

Thanks for providing the correlation IDs and detailed log information.

The logs clearly show the immediate failure: "HTTP 401 PassthroughTokenValidationFailed" with the gateway rejecting a passthrough token because the required resource-provider context wasn't available. However, you should distinguish that observed failure from the underlying root cause. The logs you've posted don't, by themselves, prove this was caused by RP registration, Conditional Access, legacy ARM tokens, or cross-tenant authentication.

First, isolate the Azure Portal/MSAL session. Sign out of all Microsoft/Azure sessions, close the browser, clear site data for portal.azure.com and Microsoft sign-in endpoints, then open a new InPrivate/Incognito session and sign in only to the affected tenant. We tested similar Azure Portal cases with the same PassthroughTokenValidationFailed error this way to eliminate stale/corrupted browser authentication state.

More importantly, test whether this is portal-specific. From a clean Azure CLI session, run:

az logout
az account clear
az login --tenant <tenant-id>
az account show
az group list --output table

If CLI/ARM operations work while the Azure Portal continues returning PassthroughTokenValidationFailed, that would strongly narrow the issue to the Portal/MSAL/resource-provider request path rather than the Azure resources themselves.

If both Portal and CLI fail, capture the Entra Sign-in logs for the same timestamps and correlate them with the request IDs you've already collected. In particular, check the application/resource, authentication result, Conditional Access result, tenant ID, and any failure code.

Also, don't decode or manipulate the Portal's access token as a fix. Access tokens are intended for the resource/API that accepts them, with the intended resource represented by the token audience; clients should generally treat access tokens as opaque.

Because your issue is reproducible and you already have exact timestamps, session IDs, and correlation IDs, if it survives a clean browser session and reproduces against ARM outside the Portal, this is a good point to open an Azure support case. Provide UTC timestamps, Tenant ID, Subscription ID, Portal session IDs, Correlation/request IDs, HTTP status and error code, Clean-browser test result, Azure CLI/ARM test result, and Relevant Entra sign-in log entries.

Microsoft can use those identifiers to correlate the failed gateway/RP requests with backend telemetry.

One other point: this error should not be confused with Microsoft Entra Pass-through Authentication (PTA). In this Azure Portal context, PassthroughTokenValidationFailed refers to validating a token passed to the resource-provider path; it doesn't, by itself, indicate a problem with the Entra Connect Pass-through Authentication agent.

References:

Microsoft identity platform - Access tokens

Similar Azure Portal pass-through token authentication case

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