Fix: Azure KeyVault 401 Unauthorized Access Error

The Error

App start:

Azure.RequestFailedException: 401 Unauthorized

Quick Fix - 1 Min

1. Local dev: az login. 2. Managed Identity: Enable on App Service. 3. KeyVault Access Policy: Grant Get/List to app. 4. Code: builder.Configuration.AddAzureKeyVault(new Uri(vaultUri), new DefaultAzureCredential())

Root Cause

App identity not authorized. Missing access policy or not logged in locally.

Related fixes: 401 in Visual Studio | 401 in Docker