feat(vault): support A2A agents wrapped as MCP tools - #6395
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August 24, 2026 14:48
This change extends the Vault plugin to work when A2A agents are invoked
via the MCP protocol (as tools in virtual servers), not just when called
directly via /a2a/{name}/invoke.
Key changes:
- vault_plugin.py: Added _load_a2a_agent_metadata() to detect A2A-backed
tools via a2a_agent_id annotation and load their system tags from the
database
- vault_plugin.py: Enhanced security - strip Authorization header when
system tag exists but no matching vault token found, preventing wrong
credentials from being forwarded
- tool_service.py: Added defense-in-depth X-Vault-Tokens stripping for
A2A tool invocation path to match REST/MCP/direct-A2A paths
- echo_mcp.py: Added MCP_ECHO_PORT environment variable support for
running multiple test server instances
- test_vault_plugin_a2a_e2e.py: Added third test validating A2A tool
wrapped as MCP tool, and fixed _wait_http() to handle SSE streams
The implementation follows the existing Vault plugin pattern for MCP
tools, with proper token injection and header stripping at both plugin
and service layers.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
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August 25, 2026 10:32
- Remove reimport of get_db in _load_a2a_agent_metadata - Use underscore placeholders for unused unpacked variables - Fixes pylint warnings: redefined-outer-name, reimported, unused-variable Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
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Aug 25, 2026
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Thanks for the PR @popagruia
Please address following blocking changes
| # | Area | File | Line | Blocking reason | Required change |
|---|---|---|---|---|---|
| 1 | Security | mcpgateway/services/tool_service.py |
6685, 6691 | When sensitive-header passthrough is enabled, headers.update(safe_headers) preserves an inbound Authorization that the Vault plugin removed on a token mismatch. prepare_a2a_invocation can also re-add configured authheaders after the pre-prepare X-Vault-Tokens strip, allowing sensitive credentials to reach the downstream A2A agent. |
Reconcile plugin output as a replacement/sanitized header set, including case-insensitive removals, rather than only updating the original map. Strip X-Vault-Tokens again after prepare_a2a_invocation as the final outbound invariant, including headers added by configured auth. |
| 2 | Security | plugins/vault/vault_plugin.py |
152, 156 | Destination-binding mismatch warnings log raw mcpServer and destination_url values. URL userinfo or query credentials can therefore be written to application logs. |
Redact userinfo, query, and fragment values before logging; log only sanitized scheme/host/path or equivalent non-secret fields. |
…ocation **Issue 1 - Headers can leak after plugin processing:** - After vault plugin strips Authorization on token mismatch, prepare_a2a_invocation() can re-add auth headers from A2A agent config - Fix: Strip X-Vault-Tokens again after prepare_a2a_invocation() as final safety invariant - This ensures sensitive headers never reach downstream regardless of plugin state **Issue 2 - URLs in logs may contain credentials:** - Warning logs at lines 152/156 could expose userinfo (user:password@) and query params - Fix: Add _sanitize_url_for_logging() helper that strips credentials before logging - Only logs scheme://host/path, never passwords or API keys in URL components Addresses security review feedback from @Lang-Akshay Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
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Security fixes applied ✅Both blocking issues have been addressed in commit 3516943: Issue 1: Header leakage after plugin processing
Issue 2: Credentials in logged URLs
Ready for re-review. Thank you @Lang-Akshay for the security review! |
added 5 commits
August 28, 2026 10:35
Two critical fixes for A2A tool invocation that caused 21 test failures: 1. **Frozen dataclass violation**: Removed redundant attempt to reassign `prepared.headers` on the frozen `PreparedA2AInvocation` dataclass. The X-Vault-Tokens header filtering was already applied before object creation (line 6691), making the post-creation assignment unnecessary and invalid. 2. **Plugin security boundary violation**: Fixed backwards logic that exposed sensitive headers (Authorization, cookies, API keys) to plugin hooks when `enable_sensitive_header_passthrough=True`. Plugins are untrusted third-party code and must ALWAYS receive filtered headers, regardless of the downstream passthrough setting. The passthrough setting controls only what reaches the downstream A2A agent, not what plugins can see. Security rationale: Plugins have broad request modification access and could log, exfiltrate, or leak sensitive headers if given unfiltered access. This fix enforces defense-in-depth by treating plugins as an untrusted security boundary while still allowing trusted downstream agents to receive auth credentials when explicitly configured. Test impact: Fixes 21 failures in TestInvokeToolA2A suite. Signed-off-by: Claude Sonnet 4.5 <noreply@anthropic.com> Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
Regenerated with uv 0.12.7 (matching CI) to pick up dev-tooling version bumps (ty, ruff, uvicorn, zope-interface, etc.) that fall within the rolling 10-day exclude-newer window as of today. Fixes the alembic-check-heads pre-commit hook failing on files modified by uv run. Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
…-dataclass mutation Re-adds the defense-in-depth strip of X-Vault-Tokens after prepare_a2a_invocation(), addressing review feedback that prepare_a2a_invocation() can reintroduce auth headers from agent config or passthrough after the earlier strip point. Implemented as an in-place dict mutation on prepared.headers (matching the existing pattern in a2a_service.py) instead of reassigning the frozen PreparedA2AInvocation field directly, which previously caused a FrozenInstanceError crash on every A2A tool invocation. Also documents why plugins/vault/echo_a2a.py must be addressed via 127.0.0.1 rather than localhost: this Mac resolves localhost to ::1 first, and the gateway's SSRF-hardening DNS pinning connects to whichever address is resolved, causing spurious connection failures against an IPv4-only test server. Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
Adds a unit test for the defense-in-depth strip added in the previous commit. prepare_a2a_invocation() is mocked to return a PreparedA2AInvocation whose headers still carry X-Vault-Tokens, so the test exercises the deletion branch directly rather than relying on a real leak path (none of which currently reach that header name). Raises PR diff coverage on tool_service.py from 66.7% to 100%, fixing the CI diff-cover gate. Signed-off-by: popagruia <adrian.popa@ro.ibm.com>
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Thanks @Lang-Akshay — both items are addressed. #1: #2: Warning logs in CI is green. Ready for another look whenever convenient. |
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Enables Vault plugin to inject bearer tokens for A2A agents invoked via MCP protocol (tools/call).
Changes:
Testing:
Closes #6394