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E_SYNCENGINE_SERVICE_AUTHENTICATION_FAILED
Within Windows cloud-file and sync-engine infrastructure, E_SYNCENGINE_SERVICE_AUTHENTICATION_FAILED reports that the signed-in identity is not authorized for the requested remote file operation. Diagnosis of this result should follow the original owner and generation rather than treating the visible symptom as the cause.
Facts that change the diagnosis
- Account and tenant identifiers.
- Token audience/scopes without secrets.
- Remote item permission result.
- Interactive sign-in and token-refresh state.
Subsystem meaning
Diagnostic focus: For E_SYNCENGINE_SERVICE_AUTHENTICATION_FAILED, isolate the service authentication exchange, account token and target tenant; filesystem repair does not fix an invalid authentication context. Keep the item identity and account fixed while changing only that boundary; a different result after that change shows which stage rejected the operation.
Authentication and authorization can fail after local placeholder lookup succeeds. Preserve account, tenant, token audience and remote item ACL evidence without logging credentials or bearer tokens.
Isolation workflow
- First: Refresh or reacquire credentials through the supported broker.
- Next: Confirm the item belongs to the same account context.
- Then: Test a known accessible item.
- Finally: Surface reauthentication when silent renewal is not permitted.
Avoid the tempting broad fix
PROXY_AUTHENTICATION_REQUIRED concerns the network proxy; this code concerns the storage service/account.
Do not log tokens, broaden sharing permissions, or switch accounts silently.
Expected branches
| Control | Interpretation | Hold constant |
|---|---|---|
| Same stable item ID, second supported path | A change separates local file-system/provider state from remote service state. | Keep account, remote version and client build fixed. |
Regression proof
Verify it with the original scenario, one boundary case, and one deliberate failure; success means the intended account obtains least-privilege access and inaccessible control items remain denied.
Technical references
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