Fix AAD authentication in ACA environments for RedTeam

[slister1001]

When running red team scans in ACA environments, DefaultAzureCredential fails because Azure CLI is not available. This fix allows passing an explicit credential from the RedTeam instance to get_chat_target().

Changes:

• Add credential parameter to get_chat_target() function
• Add _create_token_provider() helper to create callable from credential
• Pass self.credential from RedTeam.scan() to get_chat_target()
• Add credential field to AzureOpenAIModelConfiguration TypedDict
• Add tests for credential-based authentication paths

Auth priority: api_key > credential > use_aad_auth (DefaultAzureCredential)

Description

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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[Copilot]

Pull request overview

Summary:
This PR fixes AAD authentication failures in Azure Container Apps (ACA) environments for RedTeam operations. The fix allows passing an explicit credential from the RedTeam instance to get_chat_target(), avoiding reliance on DefaultAzureCredential which fails when Azure CLI is not available in containerized environments.

Changes:

• Added optional credential parameter to get_chat_target() function for explicit credential passing
• Modified RedTeam.scan() to pass self.credential to get_chat_target() for use in ACA environments
• Added comprehensive test coverage for credential-based authentication with different priority scenarios
• Updated AzureOpenAIModelConfiguration TypedDict to include credential field

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
azure/ai/evaluation/red_team/_utils/strategy_utils.py	Added credential parameter to get_chat_target() function with proper authentication priority handling (api_key > credential > DefaultAzureCredential). Includes code formatting improvements.
azure/ai/evaluation/red_team/_red_team.py	Modified scan() method to pass self.credential to get_chat_target(). Includes extensive code formatting improvements throughout the file.
tests/unittests/test_redteam/test_strategy_utils.py	Added three new test cases covering credential parameter usage, precedence testing, and various authentication scenarios. Includes code formatting improvements.