foundry agent cannot use key auth

[niuzheng168]

Description

foundry agent cannot use key auth

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

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Pull request overview

This pull request attempts to enable Azure CLI credential authentication for the foundry agent sample, addressing an issue where the agent couldn't use key authentication. However, the implementation is incomplete and introduces API design inconsistencies.

Changes:

• Added imports for AzureCliCredential and DefaultAzureCredential from azure.identity.aio
• Changed the credential parameter type annotation to only accept AzureCliCredential or DefaultAzureCredential
• Removed API key authentication logic and validation, hardcoding credential to AzureCliCredential()