Python: forward Azure AI Search query-source identity

[kmishra1204]

Summary

• add an optional query_source_credential to AzureAISearchContextProvider
• forward the caller's Azure AI Search authorization token on agentic Knowledge Base retrieval requests
• document the query-time identity option, add regression coverage, and record the change in the Python changelog

This addresses the Python side of #6864. The option is explicit so existing API key and managed identity flows keep their current behavior unless a caller supplies an async query-source credential.

Validation

• uv run --project python --dev --no-sync pytest -q python/packages/azure-ai-search/tests/test_aisearch_context_provider.py::TestAgenticSearch::test_minimal_reasoning_returns_results python/packages/azure-ai-search/tests/test_aisearch_context_provider.py::TestAgenticSearch::test_query_source_credential_forwards_authorization_token python/packages/azure-ai-search/tests/test_aisearch_context_provider.py::TestAgenticSearch::test_query_source_credential_requires_async_credential
• uv run --project python --dev --no-sync ruff check python/packages/azure-ai-search/agent_framework_azure_ai_search/_context_provider.py python/packages/azure-ai-search/tests/test_aisearch_context_provider.py
• uv run --project python --dev --no-sync pyright python/packages/azure-ai-search/agent_framework_azure_ai_search/_context_provider.py
• git diff --check -- python/CHANGELOG.md python/packages/azure-ai-search/README.md python/packages/azure-ai-search/agent_framework_azure_ai_search/_context_provider.py python/packages/azure-ai-search/tests/test_aisearch_context_provider.py

[Copilot]

Pull request overview

Adds an opt-in way for Python agentic Azure AI Search retrieval to forward a caller’s query-time identity (Entra token) to Knowledge Base retrieval requests, enabling document-level permission trimming scenarios without changing existing API key/managed identity defaults.

Changes:

• Added an optional query_source_credential parameter to AzureAISearchContextProvider and forwarded its token to KnowledgeBaseRetrievalClient.retrieve(...) via x_ms_query_source_authorization.
• Documented query-time identity forwarding in the package README.
• Added regression tests covering both default behavior (no header) and forwarding behavior (header present + correct scope).

Reviewed changes

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

File	Description
python/packages/azure-ai-search/agent_framework_azure_ai_search/_context_provider.py	Adds query_source_credential, obtains the Search scope token, and forwards it on agentic retrieval calls.
python/packages/azure-ai-search/tests/test_aisearch_context_provider.py	Adds assertions and a new test verifying the authorization header forwarding behavior.
python/packages/azure-ai-search/README.md	Documents the query-time user identity option and shows how to pass query_source_credential.

[kmishra1204]

Updated in bd48f59 to address the async credential feedback: the docs now say query_source_credential must be an async Azure credential, _query_source_authorization() raises a clear TypeError if a sync credential is passed, and there is regression coverage for that misuse case.

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