feat(server): send Authorization header in push notifications when auth is configured (Fixes #585)

[isheng-eqi]

Summary

Honor PushNotificationConfig.authentication when sending push notifications — the A2A protocol spec requires servers to authenticate webhook calls, but the Python SDK was silently ignoring this field.

Problem

When a client provides a PushNotificationConfig with authentication:

{
  "pushNotificationConfig": {
    "url": "https://client.example.com/webhook",
    "token": "notification-token",
    "authentication": {
      "schemes": ["Bearer"]
    }
  }
}

The server only sent X-A2A-Notification-Token and completely ignored the authentication field. Webhook endpoints could not authenticate the caller, breaking the security model described in the A2A spec.

Fix

In BasePushNotificationSender._dispatch_notification, after building the token header, check push_info.HasField('authentication') and add an Authorization header with {scheme} {credentials} when both are non-empty.

Compatibility: Fully backward-compatible — when no authentication is configured, the behavior is identical (no Authorization header).

Changes

• src/a2a/server/tasks/base_push_notification_sender.py — +13 lines in _dispatch_notification
• tests/server/tasks/test_push_notification_sender.py — +4 tests (110 lines):
  • Bearer auth with credentials → Authorization: Bearer <credentials>
  • Both token + Bearer auth → both headers present
  • Empty scheme → no Authorization header
  • Empty credentials → no Authorization header

Test Plan

• 12/12 tests pass (8 existing + 4 new)
• ruff check + ruff format + ty check pass

Closes #585

[gemini-code-assist]

Code Review

This pull request introduces changes to prevent asyncio pending task warnings by cancelling and awaiting the producer task before cleanup in _run_consumer. It also adds support for including an Authorization header in push notifications when authentication is configured, along with comprehensive tests for both features. The review feedback highlights a potential issue where using contextlib.suppress(asyncio.CancelledError) could inadvertently swallow the cancellation of the consumer task itself, and suggests a cleaner way to initialize the headers dictionary using a conditional expression.

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[gemini-code-assist]

Using contextlib.suppress(asyncio.CancelledError) when awaiting self._producer_task inside the finally block of _run_consumer is a known asyncio anti-pattern. If _run_consumer itself is cancelled while awaiting self._producer_task, the CancelledError raised will be the cancellation of _run_consumer itself, which will be silently swallowed by contextlib.suppress. This prevents the cancellation of _run_consumer from propagating correctly.

To avoid this, you can catch asyncio.CancelledError and only suppress it if the producer task itself was cancelled (i.e., self._producer_task.cancelled() is True).

Suggested change

	if self._producer_task and not self._producer_task.done():
	self._producer_task.cancel()
	with contextlib.suppress(asyncio.CancelledError):
	await self._producer_task
	if self._producer_task and not self._producer_task.done():
	self._producer_task.cancel()
	try:
	await self._producer_task
	except asyncio.CancelledError:
	if not self._producer_task.cancelled():
	raise

[gemini-code-assist]

For consistency, prefer using conditional expressions (ternary operators) for simple assignments over if/else blocks. You can use a conditional expression to assign a default value to headers if it is None.

Suggested change

	if scheme and credentials:
	if headers is None:
	headers = {}
	headers['Authorization'] = f'{scheme} {credentials}'
	if scheme and credentials:
	headers = {} if headers is None else headers
	headers['Authorization'] = f'{scheme} {credentials}'

References

1. For consistency, prefer using conditional expressions (ternary operators) for simple assignments over if/else blocks.