[Identity] Respect region env vars for non-MSAL based credentials

[pvaneck]

Currently, only MSAL confidential client based credentials allow passing in a region through the AZURE_REGIONAL_AUTHORITY_NAME. For the other non-MSAL based confidential flows, we should have parity with the MSAL ones.

I validated these changes on AKS using async WorkloadIdentityCredential with the following configurations:

1. AZURE_REGIONAL_AUTHORITY_NAME=westus2
2. MSAL_FORCE_REGION=westus2
3. AZURE_REGION_AUTHORITY_NAME=tryautodetect

[Copilot]

Pull request overview

This PR adds support for the AZURE_REGIONAL_AUTHORITY_NAME environment variable to non-MSAL-based credentials in the Azure Identity SDK, providing parity with MSAL-based credentials. The implementation allows credentials to use regional authority endpoints, which can improve performance and reliability by routing authentication traffic to region-specific endpoints.

Key changes:

• Added regional authority initialization logic to AadClientBase and both sync/async AadClient implementations
• Support for both AZURE_REGIONAL_AUTHORITY_NAME and MSAL_FORCE_REGION environment variables, with auto-discovery capability via IMDS
• Updated token URL generation to use regional authority when configured
• Added comprehensive tests covering regional authority initialization and usage scenarios

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
sdk/identity/azure-identity/azure/identity/_internal/aad_client_base.py	Added base methods for regional authority URL building, environment variable reading, and IMDS region discovery
sdk/identity/azure-identity/azure/identity/_internal/aad_client.py	Sync client now initializes regional authority in __init__ and implements region discovery logic
sdk/identity/azure-identity/azure/identity/aio/_internal/aad_client.py	Async client implements lazy regional authority initialization called on each token request, with async region discovery
sdk/identity/azure-identity/tests/test_aad_client.py	Added tests for token URL generation with regional authority and initialization logic
sdk/identity/azure-identity/tests/test_aad_client_async.py	Added async tests for regional authority in token requests, lazy initialization, and auto-discovery scenarios
sdk/identity/azure-identity/CHANGELOG.md	Documents the bug fix for regional authority environment variable support