feat: Replace DefaultAzureCredential with ManagedIdentityCredential for production

.github/skills/credential-free-dev/SKILL.md

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+---
+name: credential-free-dev
+description: |
+  Eliminate secrets and credentials from Azure applications using managed identities,
+  workload identity federation, and the Azure Identity SDK. Covers migration patterns
+  from connection strings and keys to credential-free authentication across Azure services.
+  Triggers: "credential-free", "managed identity", "workload identity federation",
+  "remove secrets", "connection string to managed identity", "DefaultAzureCredential",
+  "ManagedIdentityCredential", "passwordless", "keyless authentication", "eliminate keys".
+---
+
+# Azure Credential-Free Development
+
+Eliminate secrets and credentials from Azure applications using managed identities, workload identity federation, and the Azure Identity SDK.
+
+## Before Implementation
+
+Search `microsoft-docs` MCP for current patterns:
+- Query: "credential-free development Azure managed identity"
+- Query: "ManagedIdentityCredential [target service] [language]"
+- Verify: RBAC role names match current documentation
+
+## Core Principles
+
+1. **No secrets in code, config, or environment variables.** Use managed identities for Azure-hosted workloads. Use workload identity federation for non-Azure or CI/CD workloads.
+2. **ManagedIdentityCredential for production. DefaultAzureCredential for local dev only.** In production, use `ManagedIdentityCredential` explicitly — `DefaultAzureCredential`'s credential chain probing can cause subtle failures, latency, and silent fallback to unintended credentials. `DefaultAzureCredential` remains convenient for local development (falls through to Azure CLI / VS credentials).
+3. **System-assigned managed identity** for single-purpose resources. **User-assigned managed identity** when multiple resources share a credential or when you need pre-provisioned RBAC.
+4. **Connection strings with keys are legacy.** Every Azure service that supports Entra auth should use it. If a service requires a key, treat it as a gap to escalate, not a pattern to accept.
+5. **Least privilege always.** Grant the narrowest RBAC role that works. `Storage Blob Data Reader`, not `Storage Account Key Operator`. `db_datareader`, not `db_owner`.
+
+## When to Use Each Credential Type
+
+| Scenario | Use This | Why |
+|---|---|---|
+| App on Azure (App Service, Container Apps, Functions, VMs, AKS) | **ManagedIdentityCredential** (system or user-assigned) | Zero secrets, platform-managed rotation, Entra RBAC. Use explicit credential, not DefaultAzureCredential. |
+| CI/CD pipeline (GitHub Actions, Azure DevOps) | **Workload Identity Federation** | No secrets stored. OIDC token exchange with Entra. |
+| App on AWS/GCP calling Azure | **Workload Identity Federation** | Cross-cloud trust without shared secrets |
+| Local development | **DefaultAzureCredential** | Developer's own identity via CLI/VS fallback, no shared dev secrets |
+| Service-to-service (no Azure hosting) | **App registration + certificate** | When MI/WIF aren't possible. Certificates over secrets. |
+| Legacy app that can't change auth code | **Key Vault references** (stepping stone) | Secrets in Key Vault, not in config. Not the end state. |
+
+## Production Authentication: ManagedIdentityCredential
+
+> **Do not use `DefaultAzureCredential` in production.** Its credential chain probing
+> can cause subtle issues or silent failures. Replace it with a specific
+> `TokenCredential` implementation such as `ManagedIdentityCredential`.
+> — [Authentication best practices with the Azure Identity library](https://learn.microsoft.com/dotnet/azure/sdk/authentication/best-practices)
+
+Use `ManagedIdentityCredential` directly for Azure-hosted workloads. For user-assigned
+managed identities, pass the `client_id` (or object ID / resource ID in constrained
+environments where client ID isn't available) explicitly.
+
+## DefaultAzureCredential (Local Development Only)
+
+`DefaultAzureCredential` is convenient for local development because it automatically
+falls through to developer tool credentials. **Do not use in production.**
+
+The credential chain order and included credentials vary by language. See the authoritative per-language references:
+
+- [.NET](https://aka.ms/azsdk/net/identity/credential-chains#defaultazurecredential-overview)
+- [C++](https://aka.ms/azsdk/cpp/identity/credential-chains#defaultazurecredential-overview)
+- [Go](https://aka.ms/azsdk/go/identity/credential-chains#defaultazurecredential-overview)
+- [Java](https://aka.ms/azsdk/java/identity/credential-chains#defaultazurecredential-overview)
+- [JavaScript](https://aka.ms/azsdk/js/identity/credential-chains#defaultazurecredential-overview)
+- [Python](https://aka.ms/azsdk/python/identity/credential-chains#defaultazurecredential-overview)
+
+In production this chain introduces latency and unpredictable fallback — use `ManagedIdentityCredential` instead.
+
+### Optimize for Local Dev with `AZURE_TOKEN_CREDENTIALS`
+
+Set `AZURE_TOKEN_CREDENTIALS=dev` to disable production-grade credentials (MI, WIF, Environment)
+and only keep developer tool credentials in the chain. This prevents accidental use of
+deployed-service credentials during local development.
+
+> **Minimum SDK versions:** Python `azure-identity` 1.23.0+, .NET `Azure.Identity` 1.15.0+,
+> Java `azure-identity` 1.16.1+, JavaScript `@azure/identity` 4.11.0+, Go `azidentity` 1.10.0+,
+> C++ `azure-identity-cpp` 1.13.1+.
+>
+> See [Exclude a credential type category](https://learn.microsoft.com/azure/developer/python/sdk/authentication/credential-chains?tabs=dac#exclude-a-credential-type-category) for details.
+
+### SDK Packages
+
+| Language | Package | Install |
+|----------|---------|---------|
+| Python | `azure-identity` | `pip install azure-identity` |
+| .NET | `Azure.Identity` | `dotnet add package Azure.Identity` |
+| Java | `azure-identity` | Maven: `com.azure:azure-identity` |
+| TypeScript | `@azure/identity` | `npm install @azure/identity` |
+| Go | `azidentity` | `go get github.com/Azure/azure-sdk-for-go/sdk/azidentity` |
+| C++ | `azure-identity-cpp` | `vcpkg add port azure-identity-cpp` |
+
+### Production Pattern (All Languages)
+
+```python
+# Python — production
+from azure.identity import ManagedIdentityCredential
+credential = ManagedIdentityCredential()  # system-assigned
+# credential = ManagedIdentityCredential(client_id="<user-assigned-mi-client-id>")  # user-assigned
+client = ServiceClient(endpoint, credential=credential)
+```
+
+```csharp
+// C# — production
+var credential = new ManagedIdentityCredential();  // system-assigned
+// var credential = new ManagedIdentityCredential(ManagedIdentityId.FromUserAssignedClientId("<user-assigned-mi-client-id>"));  // user-assigned
+var client = new ServiceClient(new Uri(endpoint), credential);
+```
+
+```java
+// Java — production
+ManagedIdentityCredential credential = new ManagedIdentityCredentialBuilder().build();  // system-assigned
+// ManagedIdentityCredential credential = new ManagedIdentityCredentialBuilder()
+//     .clientId("<user-assigned-mi-client-id>").build();  // user-assigned
+ServiceClient client = new ServiceClientBuilder()
+    .endpoint(endpoint)
+    .credential(credential)
+    .buildClient();
+```
+
+```typescript
+// TypeScript — production
+import { ManagedIdentityCredential } from "@azure/identity";
+const credential = new ManagedIdentityCredential();  // system-assigned
+// const credential = new ManagedIdentityCredential({ clientId: "<user-assigned-mi-client-id>" });  // user-assigned
+const client = new ServiceClient(endpoint, credential);
+```
+
+### Local Development Pattern
+
+```python
+# Python — local dev only
+from azure.identity import DefaultAzureCredential
+credential = DefaultAzureCredential()
+client = ServiceClient(endpoint, credential=credential)
+```
+
+## Migration Pattern: Keys to Credential-Free
+
+Every migration follows the same 4 steps:
+
+1. **Enable managed identity** on your compute resource
+2. **Assign the right RBAC role** on the target resource
+3. **Replace** connection string / key with endpoint URL + `ManagedIdentityCredential` (production) or `DefaultAzureCredential` (local dev)
+4. **Remove** the key/secret from all config
+
+### Quick Reference: Service RBAC Roles
+
+| Service | Read Role | Write Role |
+|---------|-----------|------------|
+| Azure Storage (Blob) | `Storage Blob Data Reader` | `Storage Blob Data Contributor` |
+| Azure SQL Database | `db_datareader` (SQL role) | `db_datawriter` (SQL role) |
+| Azure Cosmos DB | `Cosmos DB Built-in Data Reader` | `Cosmos DB Built-in Data Contributor` |
+| Azure Service Bus | `Azure Service Bus Data Receiver` | `Azure Service Bus Data Sender` |
+| Azure Event Hubs | `Azure Event Hubs Data Receiver` | `Azure Event Hubs Data Sender` |
+| Azure Key Vault | `Key Vault Secrets User` | `Key Vault Secrets Officer` |
+| Azure App Configuration | `App Configuration Data Reader` | `App Configuration Data Owner` |
+
+> **Detailed migration code for each service:** See [references/migration-patterns.md](references/migration-patterns.md)
+
+## Workload Identity Federation (CI/CD and Cross-Cloud)
+
+When managed identity isn't available (GitHub Actions, external clouds, on-prem):
+
+1. Create an app registration in Entra
+2. Add a federated identity credential (OIDC issuer + subject)
+3. External workload exchanges its native token for an Entra access token
+4. No secrets stored, rotated, or transmitted
+
+### GitHub Actions Example
+
+```yaml
+- uses: azure/login@v2
+  with:
+    client-id: ${{ secrets.AZURE_CLIENT_ID }}
+    tenant-id: ${{ secrets.AZURE_TENANT_ID }}
+    subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
+```
+
+No `AZURE_CLIENT_SECRET` needed. The GitHub OIDC token is exchanged directly.
+
+## Common Pitfalls
+
+1. **Forgetting RBAC roles.** Enabling MI is step 1. Assigning the right role on the target resource is step 2. Most "MI doesn't work" issues are missing role assignments.
+2. **Overly broad roles.** `Contributor` on a resource group when you need `Storage Blob Data Reader` on one account.
+3. **Not testing locally.** `DefaultAzureCredential` falls through to Azure CLI. Make sure `az login` is used with the right subscription.
+4. **Using `DefaultAzureCredential` in production.** Its credential chain probing adds latency, can fall back to unintended credentials, and masks configuration errors. Use `ManagedIdentityCredential` explicitly for Azure-hosted production apps.
+5. **Mixing key and MI auth.** Some SDKs behave differently when both a connection string and a credential are provided. Pick one.
+6. **Assuming all services support MI.** Most do. Some legacy or partner services don't yet. Check the [services that support managed identities](https://learn.microsoft.com/entra/identity/managed-identities-azure-resources/managed-identities-status) list.
+7. **Not handling token refresh.** `ManagedIdentityCredential` handles refresh automatically. If caching tokens manually, respect expiry.
+8. **System-assigned when user-assigned is better.** Multiple resources needing same permissions = user-assigned MI to avoid duplicating RBAC assignments.
+
+## Reference Files
+
+| File | Contents |
+|------|----------|
+| [references/migration-patterns.md](references/migration-patterns.md) | Detailed before/after code for SQL, Storage, Cosmos DB, Service Bus, Event Hubs, Key Vault |
+| [references/acceptance-criteria.md](references/acceptance-criteria.md) | Correct/incorrect patterns for skill evaluation |

.github/skills/credential-free-dev/references/acceptance-criteria.md

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+# Acceptance Criteria: credential-free-dev
+
+**Packages**: `azure-identity` (Python), `Azure.Identity` (.NET), `@azure/identity` (TypeScript), `com.azure:azure-identity` (Java)
+**Purpose**: Skill testing acceptance criteria for credential-free development patterns
+
+---
+
+## 1. Authentication Patterns
+
+### 1.1 Production Credential Selection
+
+#### ✅ CORRECT: ManagedIdentityCredential for production
+```python
+from azure.identity import ManagedIdentityCredential
+from azure.storage.blob import BlobServiceClient
+
+credential = ManagedIdentityCredential()
+client = BlobServiceClient(
+    account_url="https://mystorageaccount.blob.core.windows.net",
+    credential=credential
+)
+```
+
+#### ✅ CORRECT: DefaultAzureCredential for local development
+```python
+from azure.identity import DefaultAzureCredential
+from azure.storage.blob import BlobServiceClient
+
+credential = DefaultAzureCredential()
+client = BlobServiceClient(
+    account_url="https://mystorageaccount.blob.core.windows.net",
+    credential=credential
+)
+```
+
+#### ❌ INCORRECT: DefaultAzureCredential in production
+```python
+# WRONG — DefaultAzureCredential's credential chain probing causes subtle failures,
+# latency, and silent fallback to unintended credentials in production.
+# Use ManagedIdentityCredential explicitly.
+from azure.identity import DefaultAzureCredential
+credential = DefaultAzureCredential()  # Don't use in production
+```
+
+#### ❌ INCORRECT: Hardcoded key in code
+```python
+from azure.storage.blob import BlobServiceClient
+client = BlobServiceClient.from_connection_string(
+    "DefaultEndpointsProtocol=https;AccountName=myaccount;AccountKey=abc123..."
+)
+```
+
+#### ❌ INCORRECT: Hardcoded client secret
+```python
+from azure.identity import ClientSecretCredential
+credential = ClientSecretCredential(
+    tenant_id="...",
+    client_id="...",
+    client_secret="hardcoded-secret-value"  # Never hardcode
+)
+```
+
+### 1.2 Environment Variables for Credentials
+
+#### ✅ CORRECT: Read from environment
+```python
+import os
+from azure.identity import ClientSecretCredential
+
+credential = ClientSecretCredential(
+    tenant_id=os.environ["AZURE_TENANT_ID"],
+    client_id=os.environ["AZURE_CLIENT_ID"],
+    client_secret=os.environ["AZURE_CLIENT_SECRET"],
+)
+```
+
+#### ❌ INCORRECT: Inline secrets
+```python
+credential = ClientSecretCredential(
+    tenant_id="12345-abcde",
+    client_id="67890-fghij",
+    client_secret="super-secret-value",
+)
+```
+
+---
+
+## 2. Service Client Initialization
+
+### 2.1 Storage Blob
+
+#### ✅ CORRECT: Endpoint URL + ManagedIdentityCredential
+```python
+client = BlobServiceClient(
+    account_url="https://myaccount.blob.core.windows.net",
+    credential=ManagedIdentityCredential()
+)
+```
+
+#### ❌ INCORRECT: Connection string with key
+```python
+client = BlobServiceClient.from_connection_string("...AccountKey=...")
+```
+
+### 2.2 Service Bus
+
+#### ✅ CORRECT: Namespace + ManagedIdentityCredential
+```python
+client = ServiceBusClient(
+    fully_qualified_namespace="my-namespace.servicebus.windows.net",
+    credential=ManagedIdentityCredential()
+)
+```
+
+#### ❌ INCORRECT: Connection string with SAS
+```python
+client = ServiceBusClient.from_connection_string("...SharedAccessKey=...")
+```
+
+### 2.3 Cosmos DB
+
+#### ✅ CORRECT: URL + ManagedIdentityCredential
+```python
+client = CosmosClient(
+    "https://myaccount.documents.azure.com:443/",
+    credential=ManagedIdentityCredential()
+)
+```
+
+#### ❌ INCORRECT: URL + primary key
+```python
+client = CosmosClient("https://myaccount.documents.azure.com:443/", "primary-key-here")
+```
+
+---
+
+## 3. RBAC Role Guidance
+
+### 3.1 Least Privilege
+
+#### ✅ CORRECT: Narrow role scoped to resource
+```
+Assign "Storage Blob Data Reader" on the specific storage account
+```
+
+#### ❌ INCORRECT: Overly broad role
+```
+Assign "Contributor" on the resource group
+```
+
+#### ❌ INCORRECT: Key operator instead of data role
+```
+Assign "Storage Account Key Operator Service Role" — this grants key access, not data access
+```
+
+---
+
+## 4. Managed Identity Selection
+
+### 4.1 System vs User-Assigned
+
+#### ✅ CORRECT: System-assigned for single-purpose
+```
+Single App Service accessing one storage account → system-assigned MI
+```
+
+#### ✅ CORRECT: User-assigned for shared permissions
+```
+Three Container Apps needing same Cosmos DB access → one user-assigned MI, one RBAC assignment
+```
+
+#### ❌ INCORRECT: System-assigned with duplicated RBAC
+```
+Three Container Apps each with system-assigned MI, each needing identical RBAC → 3x role assignments to maintain
+```
+
+---
+
+## 5. Workload Identity Federation
+
+### 5.1 GitHub Actions
+
+#### ✅ CORRECT: OIDC login without secret
+```yaml
+- uses: azure/login@v2
+  with:
+    client-id: ${{ secrets.AZURE_CLIENT_ID }}
+    tenant-id: ${{ secrets.AZURE_TENANT_ID }}
+    subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
+```
+
+#### ❌ INCORRECT: Client secret in GitHub Actions
+```yaml
+- uses: azure/login@v2
+  with:
+    creds: ${{ secrets.AZURE_CREDENTIALS }}  # Contains client_secret — use WIF instead
+```