Add forwarding hint support

Change-Id: Ie8a1d45f3abe0377a3b6c0cff08d27824b2861b1
diff --git a/src/detail/challenge-encoder.cpp b/src/detail/challenge-encoder.cpp
index 0f85fdc..c2bdd68 100644
--- a/src/detail/challenge-encoder.cpp
+++ b/src/detail/challenge-encoder.cpp
@@ -41,6 +41,7 @@
   }
   if (!issuedCertName.empty()) {
     response.push_back(makeNestedBlock(tlv::IssuedCertName, issuedCertName));
+    response.push_back(makeNestedBlock(ndn::tlv::ForwardingHint, Name(request.caPrefix).append("CA")));
   }
   response.encode();
 
@@ -81,6 +82,9 @@
         case tlv::IssuedCertName:
           state.m_issuedCertName = Name(item.blockFromValue());
           break;
+        case ndn::tlv::ForwardingHint:
+          state.m_forwardingHint = Name(item.blockFromValue());
+          break;
         case tlv::ParameterKey:
           if (readString(item) == "nonce") {
             lookingForNonce = true;