crypt32: Implement retrieving the encoded signer of a decoded signed message.

dlls/crypt32/msg.c

@@ -2410,6 +2410,20 @@ static BOOL CDecodeSignedMsg_GetParam(CDecodeMsg *msg, DWORD dwParamType,
         else
             SetLastError(CRYPT_E_INVALID_MSG_TYPE);
         break;
+    case CMSG_ENCODED_SIGNER:
+        if (msg->u.signed_data.info)
+        {
+            if (dwIndex >= msg->u.signed_data.info->cSignerInfo)
+                SetLastError(CRYPT_E_INVALID_INDEX);
+            else
+                ret = CryptEncodeObjectEx(
+                 X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, CMS_SIGNER_INFO,
+                 &msg->u.signed_data.info->rgSignerInfo[dwIndex], 0, NULL,
+                 pvData, pcbData);
+        }
+        else
+            SetLastError(CRYPT_E_INVALID_MSG_TYPE);
+        break;
     case CMSG_ATTR_CERT_COUNT_PARAM:
         if (msg->u.signed_data.info)
         {