Add a new command-line option to bitcoin-cli that allows the RPC password to be read from standard intput. The purpose of this option is to allow secure RPC password input to bitcoin-cli through an external program that is capable of disabling terminal echo.
This option works similarly to the existing -stdin option, and also works when combined with that option.
I have also written a simple ncurses based program that disables echo, gets input from the terminal and writes to standard output. I couldn’t find an existing askpass program that doesn’t require graphics libraries, since they are primarily used for getting passwords in a graphics environment. Unless someone can point out a suitable existing askpass program, I plan to submit my ncurses program to the contrib directory separately from this pull request.