feat: Add MCP parser plugin and body access infrastructure by huang195 · Pull Request #361 · rossoctl/cortex

huang195 · 2026-05-03T18:17:54Z

Summary

Add mcp-parser plugin: parses MCP JSON-RPC requests (tools/call, resources/read, prompts/get) and populates pctx.Extensions.MCP for downstream policy plugins
Add body access infrastructure across all listener modes:
- Pipeline.NeedsBody() introspects plugin capabilities
- ext_proc: two-phase processing via ModeOverride with ProcessingMode_BUFFERED
- forward/reverse proxy: conditional io.ReadAll before pipeline execution
- Startup validation rejects body-access plugins in waypoint mode (ext_authz limitation)
Add pipeline-level logging: plugin rejections (Info), plugin completion (Debug), context cancellation
Add structured logging in mcp-parser and all listener body-buffering paths

The mcp-parser is registered but NOT added to default pipelines — users opt in via YAML config. This prevents body buffering overhead for deployments that don't need MCP awareness.

Context

This is the first Phase 2 deliverable from the plugin architecture proposal. PRs #358 and #359 established the pipeline with jwt-validation and token-exchange. This PR adds the first plugin that couldn't exist without body access.

The MCP parser enables future plugins (tool-policy, audit, guardrails) to make authorization decisions at the MCP tool level — the core value proposition of the plugin architecture.

Test plan

10 unit tests for mcp-parser (all branches: tool call, resource read, prompt get, unknown method, nil/empty body, invalid JSON, missing params, capabilities, OnResponse)
3 body-buffering tests for ext_proc (inbound body deferral, outbound body deferral, no buffering when not needed)
2 body-buffering tests for forward proxy
2 body-buffering tests for reverse proxy
Full test suite passes: go test ./authlib/... ./cmd/authbridge/...
go vet clean
End-to-end: configure mcp-parser in Kind cluster, verify MCP tool calls are parsed

Assisted-By: Claude (Anthropic AI) noreply@anthropic.com

Add the mcp-parser plugin -- the first plugin that requires body access. It parses MCP JSON-RPC requests (tools/call, resources/read, prompts/get) and populates pctx.Extensions.MCP for downstream policy plugins. Body access infrastructure: - Pipeline.NeedsBody() checks if any plugin declares BodyAccess - ext_proc: two-phase processing via ModeOverride BUFFERED - forward/reverse proxy: conditional io.ReadAll before pipeline run - Startup validation rejects body-access plugins in waypoint mode The mcp-parser is registered but NOT in default pipelines -- users opt in via config. This prevents body buffering overhead for deployments that do not need MCP awareness. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: Hai Huang <huang195@gmail.com>

Prevent OOM from oversized request bodies when body-access plugins are configured. Uses http.MaxBytesReader with a 1MB limit matching Envoy's default per_stream_buffer_limit_bytes. Returns 413 for oversized bodies. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: Hai Huang <huang195@gmail.com>

Step-by-step instructions for enabling mcp-parser via the authbridge-runtime-config ConfigMap, including log verification and troubleshooting. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: Hai Huang <huang195@gmail.com>

esnible · 2026-05-03T18:58:23Z

+	"github.com/kagenti/kagenti-extensions/authbridge/authlib/pipeline"
+)
+
+type MCPParser struct{}


Could use a descriptive comment?

esnible · 2026-05-03T19:00:16Z

+## Prerequisites
+
+- A running Kagenti cluster (Kind or OpenShift) with the Ansible installer
+  completed


Does it matter what kind of Kubernetes cluster, and how Kagenti was installed?

esnible · 2026-05-03T19:02:04Z

+  completed
+- An agent namespace (e.g., `team1`) with AuthBridge sidecars injected


Suggested change

completed

- An agent namespace (e.g., `team1`) with AuthBridge sidecars injected

completed

- A namespace (e.g., `team1`) with labeled with `kagenti-enabled: "true"` for AuthBridge sidecar injection.

esnible

Clean, well-structured PR. The NeedsBody() introspection avoids buffering overhead when no plugin needs it, ext_proc uses ModeOverride to dynamically request bodies from Envoy, and forward/reverse proxy paths use MaxBytesReader for OOM protection. Waypoint startup validation is a good safety net. Test coverage is thorough — 10 unit tests for the parser, 7 body-buffering integration tests across all 3 listener modes.

Areas reviewed: Go (plugin, pipeline, all 3 listeners, main), Tests, Docs, Security
Commits: 3/3 signed-off
CI: 16/16 passing

esnible · 2026-05-03T19:10:15Z

+}
+
+func (p *bodyRecorderPlugin) Name() string { return "body-recorder" }
+func (p *bodyRecorderPlugin) Capabilities() pipeline.PluginCapabilities {


suggestion: bodyRecorderPlugin is defined identically in 3 test files (extproc, forwardproxy, reverseproxy). Consider extracting to a shared testutil package to avoid triple-maintenance. Not blocking since the type is small.

esnible · 2026-05-03T19:10:15Z

 	"net/url"

 	"github.com/kagenti/kagenti-extensions/authbridge/authlib/pipeline"
 )


suggestion: maxBodySize is defined independently in both forwardproxy and reverseproxy. If the limit ever changes, they could drift. Consider a shared constant (e.g., in pipeline or a listener/common package). Low priority since there are only two today.

esnible · 2026-05-03T19:10:15Z

+			if p.NeedsBody() {
+				slog.Debug("ext_proc: requesting body from Envoy", "direction", direction)
+				pendingHeaders = headers
+				pendingDirection = direction


suggestion: The ext_proc path relies on Envoy's per_stream_buffer_limit_bytes (default 1MB) to bound body size, unlike the forward/reverse proxy paths which enforce MaxBytesReader explicitly. If an operator changes Envoy's buffer limit, ext_proc silently accepts larger bodies. Consider documenting this assumption or adding a size check after receiving RequestBody.

esnible · 2026-05-03T19:10:15Z

 	ctx := stream.Context()
+
+	var pendingHeaders *corev3.HeaderMap
+	var pendingDirection string


nit: pendingHeaders/pendingDirection are scoped to the entire Process function but only meaningful between a RequestHeaders and RequestBody message. A brief comment noting the Envoy protocol guarantees that prevent stale state would help future readers.

- Add doc comment on MCPParser struct - Add comment explaining ext_proc pendingHeaders/pendingDirection lifecycle - Add body size enforcement in ext_proc (maxBodySize = 1MB) with test - Clarify README prerequisites: cluster type, namespace label Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: Hai Huang <huang195@gmail.com>

huang195 · 2026-05-03T23:19:43Z

All comments are addressed. Thanks @esnible!

- Add doc comment on MCPParser struct - Add comment explaining ext_proc pendingHeaders/pendingDirection lifecycle - Add body size enforcement in ext_proc (maxBodySize = 1MB) with test - Clarify README prerequisites: cluster type, namespace label Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: Hai Huang <huang195@gmail.com>

rubambiza added this to Rossoctl Issue Prioritization May 3, 2026

github-project-automation Bot moved this to Backlog in Rossoctl Issue Prioritization May 3, 2026

huang195 added 2 commits May 3, 2026 14:25

esnible reviewed May 3, 2026

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esnible approved these changes May 3, 2026

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huang195 closed this May 3, 2026

github-project-automation Bot moved this from Backlog to Done in Rossoctl Issue Prioritization May 3, 2026

huang195 reopened this May 3, 2026

huang195 merged commit ff1146e into rossoctl:main May 3, 2026
32 checks passed

huang195 deleted the feat/mcp-parser-body-access branch May 3, 2026 23:20

clawgenti mentioned this pull request May 4, 2026

Weekly Report 2026-05-04 rossoctl/rossoctl#1448

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xjacka mentioned this pull request May 4, 2026

Weekly Report 2026-05-04 rossoctl/rossoctl#1449

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clawgenti mentioned this pull request May 4, 2026

Weekly Report 2026-05-04 rossoctl/rossoctl#1450

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huang195 mentioned this pull request May 4, 2026

feat: Add A2A parser plugin for inbound request inspection #363

Merged

5 tasks

This was referenced May 15, 2026

refactor(authlib): proxy listeners session-event parity with extproc #412

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fix(weather-demo): teach pick_log_container the proxy-sidecar container name #420

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mrsabath mentioned this pull request Jun 2, 2026

epic: Plugin Pipeline: Extending AuthBridge Beyond Token Exchange rossoctl/rossoctl#1458

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9 tasks

huang195 mentioned this pull request Jun 24, 2026

track(merged): feat: Add MCP parser plugin and body access infrastructure (ext#361) #550

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feat: Add MCP parser plugin and body access infrastructure#361

feat: Add MCP parser plugin and body access infrastructure#361
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huang195 commented May 3, 2026

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