first pass on keyfile helper

cmd/createkeyfile/main.go

@@ -0,0 +1,96 @@
+package main
+
+/*
+
+The purpose of this command is to be run as a new user. It initializes their ssh authorized_keys2 file, which allows them to ssh in for the first time.
+
+This is an isolated command because creating a file and chowning it normally requires root permissions. We don't want to run the welcome command as root, so we give it `sudo` permission to run this one command as any user. The keyfile path is hardcoded, so if someone were to assume `welcome`'s identity, it could of course cause havoc but not delete
+
+This is a port of the old createkeyfile.py script from the former admin system.
+
+There are two functional changes:
+
+1. It also creates `.ssh`. I can't remember if there was a reason the old script didn't do that as there is no record one way or the other. But having this command make `.ssh` means one fewer thing in the sudoers file.
+
+2. It guards against overwriting of both .ssh and authorized_keys2. This is solely to limit the effect of a security breach. In the old admin system keys were managed via the django admin, meaning this script was used to add keys to authorized_keys2. these days we just edit authorized_keys2 directly, so this new command should only ever be used to initialize .ssh for a new user.
+
+*/
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+	"path"
+)
+
+const keyfileName = "authorized_keys2"
+
+func quit(msg string) {
+	fmt.Println(msg)
+	os.Exit(1)
+}
+
+func main() {
+	u, err := user.Current()
+	if err != nil {
+		quit(err.Error())
+	}
+
+	sshPath := path.Join("/home", u.Username, ".ssh")
+	keyfilePath := path.Join(sshPath, keyfileName)
+
+	if err = os.Mkdir(sshPath, os.FileMode(0600)); err != nil {
+		quit(err.Error())
+	}
+
+	f, err := os.Create(keyfilePath)
+	if err != nil {
+		quit(err.Error())
+	}
+
+	defer f.Close()
+
+	if err = os.Chmod(keyfilePath, os.FileMode(0600)); err != nil {
+		quit(err.Error())
+	}
+
+	stdin := []byte{}
+
+	n, err := os.Stdin.Read(stdin)
+	if err != nil {
+		quit(err.Error())
+	} else if n == 0 {
+		quit("nothing passed on STDIN")
+	}
+
+	n, err = f.Write(stdin)
+	if err != nil {
+		quit(err.Error())
+	} else if n == 0 {
+		quit("wrote nothing to keyfile")
+	}
+}
+
+/*
+
+The old script, in full:
+
+#!/usr/bin/env python3
+"""this script allows django to add public keys for a user. it's in its own
+script so that a specific command can be added to the ttadmin user's sudoers
+file."""
+import sys
+
+KEYFILE_PATH = '/home/{}/.ssh/authorized_keys2'
+
+
+def main(argv):
+    username = argv[1]
+    with open(KEYFILE_PATH.format(username), 'w') as f:
+        f.write(sys.stdin.read())
+
+
+if __name__ == '__main__':
+    exit(main(sys.argv))
+
+*/