In the documentation (https://blockchain.info/api/json_rpc_api) I see -rpcssl Set to use a secure connection (Recommended), how can I set this in the code above? Thanks for the info about url encode 
As far as I know, when you specify "https://" you should automatically connect with SSL enabled (I'm not a PHP programmer). You can check it by connecting to non-ssl site (e.g. you own local webserver) using "https://" prefix, if it gives error then it works fine.