TAIP-15: Add explicit connectionTypes and trust connection support

[martindejonge1981-collab]

Summary

This PR extends TAIP-15 (Agent Connection Protocol) with explicit connectionTypes field for all connections and adds support for trust connections (DDQ exchange, mutual trust, whitelisting).

Breaking Changes

Added REQUIRED connectionTypes field

All Connect messages now REQUIRE a connectionTypes array specifying connection purpose:

• ["transaction"] - For transactional connections (existing use case)
• ["ddq-access"] - For DDQ document exchange
• ["mutual-trust"] - For bilateral trust relationships
• ["whitelist"] - For straight-through processing

Why This Breaking Change?

1. Explicit is better than implicit - Type should be declared, not inferred
2. Better validation - Clear error messages and schema support
3. Standards alignment - Follows JSON-LD, OpenAPI, GraphQL patterns
4. Easier to extend - New types can be added without field detection logic
5. Self-documenting - Single field declares connection purpose

Migration

Old (TAIP-15 before this update):

{
  "requester": {...},
  "principal": {...},
  "agents": [...],
  "constraints": {...}
}

New (add one field):

{
  "connectionTypes": ["transaction"],  // Add this line
  "requester": {...},
  "principal": {...},
  "agents": [...],
  "constraints": {...}
}

New Features: Trust Connections

VASPs can now establish institutional trust relationships:

Connection Types

1. transaction - Transactional connections (existing, now explicit)

   • Requires: requester, principal, agents, constraints
   • Use: B2B integrations, recurring billing, AI agents

2. ddq-access - DDQ document exchange

   • No requester/principal/agents/constraints needed
   • Use: Compliance verification, initial due diligence

3. mutual-trust - Bilateral trust relationships

   • Reduces verification requirements
   • Use: Established business relationships

4. whitelist - Straight-through processing

   • Pre-approved automatic transaction processing
   • Use: High-volume trusted counterparties

Typical Trust Progression

ddq-access → mutual-trust → whitelist

TAIP-4 Extensions (Non-Breaking)

Added optional fields to Authorize message for trust connection approval:

• approvedTypes: Array of approved connection types
• ddqDocument: DDQ document reference object
• trustLevel: Trust status indicator

These fields are only used when responding to trust-based Connect messages.

Files Modified

• ✅ TAIPs/taip-15.md - Major update with breaking changes
• ✅ TAIPs/taip-4.md - Added connection-specific fields
• ✅ messages.md - Updated Connect and Authorize tables
• ✅ CHANGELOG.md - Documented breaking changes
• ❌ TAIPs/taip-20.md - Deleted this draft (merged into TAIP-15)

Validation Rules

// connectionTypes is REQUIRED
if (!connectionTypes || connectionTypes.length === 0) {
  throw new Error("connectionTypes is required");
}

// Transactional connections need full structure
if (connectionTypes.includes("transaction")) {
  if (!requester || !principal || !agents || !constraints) {
    throw new Error("Transactional connections require requester, principal, agents, and constraints");
  }
}

// Trust connections should be agent to agent
if (connectionTypes.some(t => ["ddq-access", "mutual-trust", "whitelist"].includes(t))) {
  if (requester || principal || agents || constraints) {
    console.warn("Trust connections should not include transactional fields");
  }
}

Discussion Points

• Use explicit connectionTypes for all connections (decided: YES)
• Should DDQ documents support DIDComm attachments?

Implementation Impact

Existing TAIP-15 implementations must:

1. Add connectionTypes: ["transaction"] to all Connect messages
2. Update validation to check connectionTypes field
3. No other changes needed

New trust connection implementations:

1. Use appropriate connectionTypes values
2. Omit requester/principal/agents/constraints
3. Handle new Authorize response fields

Timeline

TAIP-15 is currently in "Review" status, making this the appropriate time for breaking changes before reaching "Final" status.

Checklist

• TAIP-15 updated with explicit connectionTypes
• TAIP-4 extensions documented
• messages.md updated
• CHANGELOG updated with breaking changes
• TAIP-20 draft removed (merged into TAIP-15)
• Test vectors updated (will add based on feedback)