/azure-prepare

Azure Authentication Best Practices

Source: Microsoft — Passwordless connections for Azure services and Azure Identity client libraries.

Golden Rule

Use managed identities and Azure RBAC in production. Reserve DefaultAzureCredential for local development only.

Authentication by Environment

Why Not DefaultAzureCredential in Production?

1. Unpredictable fallback chain — walks through multiple credential types, adding latency and making failures harder to diagnose.
2. Broad surface area — checks environment variables, CLI tokens, and other sources that should not exist in production.
3. Non-deterministic — which credential actually authenticates depends on the environment, making behavior inconsistent across deployments.
4. Performance — each failed credential attempt adds network round-trips before falling back to the next.

Production Patterns

.NET

using Azure.Identity;

var credential = Environment.GetEnvironmentVariable("AZURE_FUNCTIONS_ENVIRONMENT") == "Development"
    ? new DefaultAzureCredential()                          // local dev — uses CLI/VS credentials
    : new ManagedIdentityCredential();                      // production — deterministic, no fallback chain
// For user-assigned identity: new ManagedIdentityCredential("<client-id>")

TypeScript / JavaScript

import { DefaultAzureCredential, ManagedIdentityCredential } from "@azure/identity";

const credential = process.env.NODE_ENV === "development"
  ? new DefaultAzureCredential()                          // local dev — uses CLI/VS credentials
  : new ManagedIdentityCredential();                      // production — deterministic, no fallback chain
// For user-assigned identity: new ManagedIdentityCredential("<client-id>")

Python

import os
from azure.identity import DefaultAzureCredential, ManagedIdentityCredential

credential = (
    DefaultAzureCredential()                              # local dev — uses CLI/VS credentials
    if os.getenv("AZURE_FUNCTIONS_ENVIRONMENT") == "Development"
    else ManagedIdentityCredential()                      # production — deterministic, no fallback chain
)
# For user-assigned identity: ManagedIdentityCredential(client_id="<client-id>")

Java

import com.azure.identity.DefaultAzureCredentialBuilder;
import com.azure.identity.ManagedIdentityCredentialBuilder;

var credential = "Development".equals(System.getenv("AZURE_FUNCTIONS_ENVIRONMENT"))
    ? new DefaultAzureCredentialBuilder().build()          // local dev — uses CLI/VS credentials
    : new ManagedIdentityCredentialBuilder().build();      // production — deterministic, no fallback chain
// For user-assigned identity: new ManagedIdentityCredentialBuilder().clientId("<client-id>").build()

Local Development Setup

DefaultAzureCredential is ideal for local dev because it automatically picks up credentials from developer tools:

1. Azure CLI — az login
2. Azure Developer CLI — azd auth login
3. Azure PowerShell — Connect-AzAccount
4. Visual Studio / VS Code — sign in via Azure extension

import { DefaultAzureCredential } from "@azure/identity";

// Local development only — uses CLI/PowerShell/VS Code credentials
const credential = new DefaultAzureCredential();

Environment-Aware Pattern

Detect the runtime environment and select the appropriate credential. The key principle: use DefaultAzureCredential only when running locally, and a specific credential in production.

Tip: Azure Functions sets AZURE_FUNCTIONS_ENVIRONMENT to "Development" when running locally. For App Service or containers, use any environment variable you control (e.g. NODE_ENV, ASPNETCORE_ENVIRONMENT).

import { DefaultAzureCredential, ManagedIdentityCredential } from "@azure/identity";

function getCredential() {
  if (process.env.NODE_ENV === "development") {
    return new DefaultAzureCredential();          // picks up az login / VS Code creds
  }
  return process.env.AZURE_CLIENT_ID
    ? new ManagedIdentityCredential(process.env.AZURE_CLIENT_ID)  // user-assigned
    : new ManagedIdentityCredential();                            // system-assigned
}

Security Checklist

• Use managed identity for all Azure-hosted apps
• Never hardcode credentials, connection strings, or keys
• Apply least-privilege RBAC roles at the narrowest scope
• Use ManagedIdentityCredential (not DefaultAzureCredential) in production
• Store any required secrets in Azure Key Vault
• Rotate secrets and certificates on a schedule
• Enable Microsoft Defender for Cloud on production resources

Further Reading

• Passwordless connections overview
• Managed identities overview
• Azure RBAC overview
• .NET authentication guide
• Python identity library
• JavaScript identity library
• Java identity library