Why should local authentication be disabled for Azure services such as Event Grid and Cognitive Services?

Azure services work better when authentication is handled by Microsoft Entra, not by long-lived service keys. Local authentication creates a separate trust path that is harder to govern, easier to overuse, and more likely to survive role changes, app refactors or personnel turnover. For services such as Event Grid and Cognitive Services, the safer pattern is to remove shared secrets wherever the platform supports Entra-based access.

A good way to think about this is blast radius. A local key often works anywhere the service accepts it, which makes it difficult to scope by workload, environment or operator role. Entra access lets you use centrally managed identities and policy-driven access decisions instead of distributing a credential that can quietly outlive the reason it was issued. That is especially important for services that may be integrated into many apps and automation paths at once.

Local authentication also complicates rotation and revocation. If a key is copied into pipelines, scripts, configuration files or third-party tools, it becomes easy to miss one of the places where it was stored or cached. Central identity reduces that hidden persistence because access can be changed at the identity layer rather than by chasing every copy of a secret. For Azure architecture guidance around Entra roles, managed identities and secret reduction, see the Microsoft Azure Security Guide.

Services that accept local auth are also attractive to attackers because a valid key can function like a reusable bearer credential. If an operator account is removed, a workload is retired, or a contractor leaves, the secret may still work unless it is explicitly found and revoked. That is why inventory matters: the security issue is not just whether a key exists, but whether anyone still depends on it and whether you can prove every remaining use case is intentional.

When you can, migrate to Entra-based access and treat local auth as an exception path. The practical goal is to reduce the number of credentials that can independently authorize access to production services. In Azure environments, that usually means replacing static keys with managed identities, scoped roles and federated patterns where possible, then eliminating the leftover secret-based paths one service at a time.

Cloud service credentials are a common compromise path, not because the service is weak by itself, but because shared secrets are easy to copy and hard to fully inventory. Historical cloud incidents show how stolen or lingering credentials can be reused long after the original administrative context has changed, which is exactly why local auth should be phased out rather than merely documented. See the Storm-1283 OAuth apps abuse 2023 case for how app credentials can be turned into ongoing cloud abuse, and the Dropbox Sign breach 2024 for the operational consequences of a compromised back-end service account.

For teams standardising Azure access, the key decision is whether a service still needs a service-specific secret at all. If the answer is yes, that should be treated as a temporary constraint with explicit ownership, rotation and retirement criteria, not as the default operating model. If the answer is no, local authentication should be removed and any residual secret use should be tracked as technical debt.

Risk and Threat Considerations

Local authentication increases exposure because one leaked or over-broad key can unlock a cloud service independently of normal identity controls. It also creates hidden persistence, since copied secrets may remain active in code, pipelines or third-party integrations after the original user or workload has changed.

Failure mechanism: A service-specific key bypasses centralized access governance, so revocation, scoping and accountability depend on manual discovery rather than policy-managed identity.

Impact: An attacker or former insider who obtains the key may retain access to the service until every stored copy is found and removed, which can extend compromise windows and complicate incident response.

Practitioner Guidance

What to verify: Confirm whether each Azure service is actually using local auth for production traffic, and map every place that credential is stored or injected. If you cannot inventory all consumers of the key, you cannot safely claim it is controlled.

Decision rule: If the service supports Microsoft Entra access for the required use case, make that the default and reserve local auth only for a documented exception with an expiry date. If a workload still needs a secret, treat the secret as a migration gap, not a steady state.

What practitioners underestimate: The hardest part is usually not enabling Entra, but finding the forgotten consumers, such as scripts, build jobs and partner integrations. Those hidden dependencies are where local auth tends to survive longest.

Practitioner takeaway: The real control objective is not just stronger authentication, it is removing credential paths that cannot be centrally governed, quickly revoked and confidently inventoried.

Related resources from NHI Mgmt Group

• Why do collaboration tools create such a large secrets risk?
• Why do leaked secrets remain such a persistent NHI risk?
• What makes idle secrets such a serious NHI risk?
• Why do local or private-network AI and data science services still need real authentication controls?