For passwords, you should include pscp.exe with your app and call it instead of using scp (as a bonus it would work in Win7 and Win8.x too). Use -pw for that.
pscp.exe (an SCP client, i.e. command-line secure file copy)
64-bit x86: pscp.exe (signature)
64-bit Arm: pscp.exe (signature)
32-bit x86: pscp.exe (signature)