Unfortunately, the Google Cast protocol does not support password protection at this time. In AirServer Universal and AirServer for Mac, it's only possible to set a password for AirPlay devices.

However, when using AirServer Windows 10 Desktop Edition, AirServer for Xbox One and AirServer Connect 4K UHD, you can configure a prompt to appear before allowing an Android device to cast. You can do this by opening up the on-screen settings from the hamburger menu, selecting Google Cast and then setting it to require a prompt.