Sign a message with the private key of an address. The address must be a P2PKH address.
addressstringREQUIREDmessagestringREQUIREDcurl --user myuser --data-binary '{"jsonrpc":"1.0","id":"1","method":"signmessage","params":["1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX","my message"]}' -H 'content-type:text/plain;' http://127.0.0.1:8332/"H3/9bEPGhd0THi...base64_signature..."