Add bin/setpasswd to set user password

.gitignore

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+/user.txt

bin/setpasswd

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+#!/usr/bin/env ruby
+
+require "digest"
+require "fileutils"
+require "io/console"
+require "securerandom"
+
+print "User name: "
+username = $stdin.gets.chomp
+
+unless username =~ /^[a-zA-Z0-9_]+$/
+  $stderr.puts "Invalid characters in user name"
+  exit(1)
+end
+
+print "Password: "
+password = $stdin.noecho(&:gets).chomp
+
+user_path = File.join(File.dirname(__FILE__), "../user.txt")
+
+salt = SecureRandom.random_bytes(8)
+salthex = salt.chars.map {|c| sprintf("%02X", c.ord)}.join
+input = salt + password
+hash = Digest::SHA256.hexdigest(input)
+hashhex = hash.chars.map {|c| sprintf("%02X", c.ord)}.join
+user_file_contents = "#{username}:#{salthex}:#{hashhex}\n"
+
+File.binwrite(user_path, user_file_contents)
+puts "User and password set"