mcp-gateway

Overview ¶

Package main implements the MCP gateway service.

Request filter pipeline ¶

Every inbound request is processed through a fixed ordered pipeline of five stages before audit/analytics finalization runs unconditionally as stage 6. Stage order is security-sensitive and is fixed in code:

Stage 1 – InspectFilter:   bounded body capture; RPC method and tool name extraction
Stage 2 – PolicyFilter:    atomic policy snapshot acquisition; OAuth metadata early-exit
Stage 3 – AuthFilter:      optional OAuth and adapter-certificate authentication
Stage 4 – AuthzFilter:     authorization and session/grant evaluation
Stage 5 – UpstreamFilter:  credential cleanup; path rewrite; upstream proxy
Stage 6 – (orchestrator):  audit/analytics finalization

Ordering guarantees:

• Authentication (stage 3) always completes before authorization (stage 4).
• The policy snapshot (stage 2) is captured once and held immutable for the entire exchange lifetime; no later stage may re-acquire it.
• Authorization inputs (Policy and Identity on Exchange) must not be mutated after the authz stage sets Decision; upstream preparation (stage 5) only reads them.

Each filter returns Continue, Reject, or Respond. On any non-Continue result the pipeline halts and stage 6 runs from the orchestrator.