Allow overriding ICE ufrag and pwd fields

Adds two new optional config keys - `iceUfrag` and `icePwd` which
are passed to libjuice.

Refs: paullouisageneau#1166

include/rtc/configuration.hpp

@@ -93,6 +93,10 @@ struct RTC_CPP_EXPORT Configuration {
 	optional<string> certificatePemFile;
 	optional<string> keyPemFile;
 	optional<string> keyPemPass;
+
+	// Overriding ICE ufrag/pwd
+	optional<string> iceUfrag;
+	optional<string> icePwd;
 };
 
 #ifdef RTC_ENABLE_WEBSOCKET

src/impl/icetransport.cpp

@@ -130,10 +130,16 @@ IceTransport::IceTransport(const Configuration &config, candidate_callback candi
 	}
 
 	// Create agent
-	mAgent = decltype(mAgent)(juice_create(&jconfig), juice_destroy);
-	if (!mAgent)
+	auto agent = juice_create(&jconfig);
+	if (!agent)
 		throw std::runtime_error("Failed to create the ICE agent");
 
+	if (config.iceUfrag && config.icePwd) {
+		juice_set_local_ice_attributes(agent, (char*)config.iceUfrag->c_str(), (char*)config.icePwd->c_str());
+	}
+
+	mAgent = decltype(mAgent)(agent, juice_destroy);
+
 	// Add TURN servers
 	for (const auto &server : servers)
 		if (!server.hostname.empty() && server.type != IceServer::Type::Stun)