chore: add mpc signing response type

Ticket: WP-4759

Author: pranavjain97

src/api/enclaved/signMpcTransaction.ts

@@ -68,8 +68,7 @@ interface EddsaSigningParams {
 }
 
 export async function signMpcTransaction(req: EnclavedApiSpecRouteRequest<'v1.mpc.sign', 'post'>) {
-  const { source, pub, encryptedDataKey } = req.decoded;
-  const { coin: coinName, shareType } = req.params;
+  const { source, pub, coin, encryptedDataKey, shareType } = req.decoded;
 
   if (!source || !pub) {
     throw new Error('Source and public key are required for MPC signing');
@@ -80,7 +79,7 @@ export async function signMpcTransaction(req: EnclavedApiSpecRouteRequest<'v1.mp
   }
 
   const bitgo = req.bitgo;
-  const coin = bitgo.coin(coinName);
+  const coinInstance = bitgo.coin(coin);
 
   // Get private key from KMS
   const prv = await retrieveKmsPrvKey({ pub, source, cfg: req.config });
@@ -92,11 +91,11 @@ export async function signMpcTransaction(req: EnclavedApiSpecRouteRequest<'v1.mp
   }
 
   try {
-    const mpcAlgorithm = coin.getMPCAlgorithm?.() || MPCType.ECDSA; // Default to ECDSA if method doesn't exist
+    const mpcAlgorithm = coinInstance.getMPCAlgorithm?.() || MPCType.ECDSA; // Default to ECDSA if method doesn't exist
 
     if (mpcAlgorithm === MPCType.EDDSA) {
       return await handleEddsaSigning(req.bitgo, req.config, {
-        coin,
+        coin: coinInstance,
         shareType,
         txRequest: req.decoded.txRequest,
         prv,

src/enclavedBitgoExpress/routers/enclavedApiSpec.ts

@@ -96,8 +96,24 @@ const SignMpcRequest = {
 
 // Response type for /mpc/sign endpoint
 const SignMpcResponse: HttpResponse = {
-  // TODO: Define proper response type for MPC transaction signing
-  200: t.any,
+  // Response type for MPC transaction signing
+  200: t.union([
+    // Commitment share response
+    t.type({
+      userToBitgoCommitment: t.any,
+      encryptedSignerShare: t.any,
+      encryptedUserToBitgoRShare: t.any,
+      encryptedDataKey: t.string,
+    }),
+    // R share response
+    t.type({
+      rShare: t.any,
+    }),
+    // G share response
+    t.type({
+      gShare: t.any,
+    }),
+  ]),
   500: t.type({
     error: t.string,
     details: t.string,