How a Missing Setting Breaks Azure Token Providers in Tests

Most Azure SDK components rely on configuration values to know how to authenticate. For example:

new AzureServiceTokenProvider(
    config["Authentication:AzureServiceAuthConnectionString"]
);

If this key is missing, the Azure SDK does not stop. Instead, it thinks:
“I’ll figure this out myself!”

And then it tries fallback authentication options, such as:

• Developer login credentials
• Azure CLI authentication
• Managed Identity lookups
• Subscription scans

These attempts fail instantly inside a local test environment, leading to confusing “AccessDenied” messages.
The surprising part?
Your project may work fine during normal execution—but your API project or test project may simply be missing the same setting.

This tiny configuration mismatch means:

• Unit tests succeed
• API runs fine locally
• Integration tests fail dramatically

Once you understand this, the solution becomes much clearer.