UTC — Universal Tool-Calling Layer

Call the same tool from MCP, REST, or A2A with one WIMSE token and one audit trail. The Universal Tool-Calling Layer (UTC) normalizes whatever arrives on the wire, verifies it once, and applies the same revocation and audience rules everywhere.

Why it’s worth your time

• One registration, many clients — agents pick the protocol their framework supports; you do not re-register or re-policy per wire format.
• Same security story as MCP — confused-deputy checks, audience binding, and kill-switch revocation apply to every adapter.
• Off the exchange path — UTC sits in front of your tool handlers; token exchange latency stays unchanged.

How it works

Platform credential  →  POST /v1/exchange/token  →  WIMSE JWT
                              ↓
                    UTC middleware (your tool server)
                    adapter → verify → allow / deny
                              ↓
                         tool handler

Adapters translate native requests into one ToolCallRequest. A single Verifier checks token, audience, and revocation regardless of protocol.

Adapter	Detects
MCP	JSON-RPC tools/call
HTTP	REST paths + Bearer token
A2A	Agent-to-agent task shapes

Register tools with optional protocol scope — an MCP-only tool returns 403 on REST even when the token is valid.

Wire it up

1. Exchange a platform credential for a WIMSE JWT — token exchange.
2. Register the tool on the PEP (resource URI + allowed protocols) — MCP security covers PEP-side registration.
3. Mount UTC middleware on your tool server — pkg/toolcall.
4. Point JWKS resolution at GET /v1/identity/jwks on your fabric unit.

MCP:

curl -s -X POST "$TOOL_URL/" \
  -H 'Content-Type: application/json' \
  -H "Authorization: Bearer $WIMSE_JWT" \
  -d '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"search","arguments":{"q":"starfly"}},"id":1}'

HTTP (same token, same tool):

curl -s "$TOOL_URL/api/search?q=starfly" \
  -H "Authorization: Bearer $WIMSE_JWT"

What you should see

Scenario	Result
MCP or HTTP with valid token	Same subject, same tool_id, protocol recorded in audit
Valid token, wrong protocol	403 capability_denied
Token for tool A at tool B	403 audience mismatch

Code in this repo

Path	Status
pkg/toolcall/	Shipped — middleware, verifier, adapters
examples/multi-protocol-tool/	Preview — demo export pending

Related

• MCP security — register and verify on the PEP
• Exchange · Revocation — fabric invariants
• Documentation voice — how these pages are written