Gets a IotHub Message's properties item. No new memory is allocated, the caller is not responsible for freeing the memory. The memory is valid until IoTHubMessage_Destroy is called on the message.
const char* IoTHubMessage_GetProperty( IOTHUB_MESSAGE_HANDLE iotHubMessageHandle, const char * key );
iotHubMessageHandleHandle to the message.
keyname of the property to retrieve.
A string with the property's value, or NULL if it does not exist in the properties list.