[Identity] Emit warning in EnvironmentCredential for user/pass

[pvaneck]

If UsernamePasswordCredential environment variables are detected in EnvironmentCredential and DefaultAzureCredential, we now ensure that a warning noting its deprecation is emitted with the correct stacklevel that point's to the user's credential instantiation.

Without this, by default, the user won't see the warning emitted in the UsernamePasswordCredential initializer if UsernamePasswordCredential wasn't directly instantiated by the user.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[Copilot]

Pull Request Overview

This PR introduces deprecation warnings for the usage of UsernamePasswordCredential when it is indirectly instantiated through EnvironmentCredential. Key changes include:

• Adding a new test to verify that the deprecation warning is emitted with the correct stacklevel.
• Updating the UsernamePasswordCredential to conditionally emit a deprecation warning based on a silencing flag.
• Emitting a deprecation warning from EnvironmentCredential with an appropriate stacklevel.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
sdk/identity/azure-identity/tests/test_environment_credential.py	Adds a test for the deprecation warning behavior.
sdk/identity/azure-identity/azure/identity/aio/_credentials/environment.py	Updates docstring to remove legacy authentication method reference.
sdk/identity/azure-identity/azure/identity/_credentials/user_password.py	Inserts conditional deprecation warning logic.
sdk/identity/azure-identity/azure/identity/_credentials/environment.py	Inserts a deprecation warning emission with dynamic stacklevel.

Comments suppressed due to low confidence (1)

sdk/identity/azure-identity/azure/identity/_credentials/environment.py:104

• The warning message contains a grammatical error in the phrase 'as is it doesn't support multifactor authentication'. Please update it to 'as it doesn't support multifactor authentication'.

warnings.warn("Environment is configured to use username and password authentication. This authentication method is deprecated, as is it doesn't support multifactor authentication (MFA). For more details, see https://aka.ms/azsdk/identity/mfa.", DeprecationWarning, stacklevel=3 if within_dac.get() else 2)