CIP-56/ERC-20 Middleware - #453 - Milestone 2: Middleware Service (Ethereum JSON-RPC API + supporting libraries)

Milestone 2: Middleware Service (Ethereum JSON-RPC API + supporting libraries)

• Scope:
  • Ethereum JSON-RPC API Server (pkg/ethrpc/, cmd/api-server/): MetaMask-compatible JSON-RPC server implementing the eth_*, net_*, and web3_* method namespaces required for EVM wallet, dapp, indexer, and explorer interoperability.
  • Transaction Orchestration Engine: EVM-calldata → Canton-command translation, executed via Interactive Submission (PrepareSubmission → sign → ExecuteSubmission).
  • Identity, Auth, and Onboarding: user registration via EIP-191 signatures, external-party allocation, JWT session management, EVM-signature verification (pkg/auth/, pkg/registration/).
  • Pluggable Signer interface (pkg/cantonsdk/token/types.go) with signature SignDER(message []byte) ([]byte, error) and Fingerprint() (string, error), wired through a KeyResolver callback in pkg/app/api/server.go so signer implementations are selected at API server initialization time. This milestone ships one concrete implementation (CantonKeyPair in pkg/keys/canton_keys.go) backed by custodial secp256k1 keys with AES-256-GCM encryption at rest. The interface is designed to accept additional implementations without orchestrator changes: Milestones 5–6 add Snap-backed and institutional-custody-backed signers behind the same interface, selectable per deployment, per tenant, or per user.
  • Splice Registry client (pkg/registry/) for wallet TransferFactory discovery.
  • Contract State Resolver: token + holding + bridge state resolution for transaction construction and EVM-shaped receipts.
  • Indexer Integration Adapter: balance, holdings, and event queries served from the indexer backend.
  • Infrastructure as Code: containerisation (Docker), Kubernetes manifests, configuration, observability.