#!/bin/bash

chdir=0
kerberos=0
x11=0
while getopts ":kx" opt; do
  case $opt in
    c) chdir=1;;
    k) kerberos=1;;
    x) x11=1;;
  esac
done
shift $((OPTIND-1))

user="$1"; shift
if [ -z "$user" ]; then
  echo >&2 "Usage: become [-c] [-k] [-x] <user>"
  echo >&2 "Options: -c   Stay in current directory even if target user is not root."
  echo >&2 "         -k   Delegate Kerberos credentials even if target user is not root."
  echo >&2 "         -x   Delegate X11 cookie even if target user is not root."
  exit 1
fi

uid=$(PATH=/usr/xpg4/bin:/usr/bin id -u "$user" 2>/dev/null)
if [ -z "$uid" ]; then
  echo >&2 "Who is $user?"
  exit 2
fi

if [ $uid = 0 ]; then
  chdir=1
  kerberos=1
  x11=1
fi

PRINCIPAL=$(klist 2>/dev/null | sed -n 's/^Default principal: //p')
if [ $x11 = 1 -a -n "$DISPLAY" -a "${DISPLAY##localhost:}" = "$DISPLAY" ]; then
  COOKIE="$(xauth list $DISPLAY)"
fi
ignore_profile_user=0
for candidate in "$HOME" "$PROFILE_HOME"; do
  [ -n "$candidate" ] || continue
  BECOME="$candidate/.become"
  [ -d "$BECOME" ] || continue

  # Script to run when becoming any user.
  [ -z "$allusersprofile" ] && allusersprofile="$BECOME/all"
  [ -f "$allusersprofile" ] || allusersprofile=

  # Set $HOME/all sticky to ignore $PROFILE_HOME/$user.
  if [ "$candidate" = "$HOME" ]; then
    [ -k "$BECOME/all" ] && ignore_profile_user=1
  else
    [ $ignore_profile_user = 1 ] && continue
  fi

  # Script to run (after the one mentioned above) when becoming this user.
  [ -z "$userprofile" ] && userprofile="$BECOME/$user"
  [ -f "$userprofile" ] || userprofile=
done

file="${TMPDIR:-/tmp}/$USER.become.$user.$RANDOM.$$"
umask=$(builtin umask -p)
builtin umask 077
if exec 3>"$file" && exec <"$file" && rm "$file"; then
  builtin $umask
  echo >&3 "cd"
  echo >&3 "PROFILE_HOME='${PROFILE_HOME:-$HOME}'"
  if [ -n "$PRINCIPAL" ]; then
    echo >&3 "PRINCIPAL='$PRINCIPAL'"
    if [ $kerberos = 1 ]; then
      ccname=$(klist 2>/dev/null | sed -n 's/^Ticket cache: [DF]I[LR][E:]://p')
      if [ -f "$ccname" ]; then
        echo >&3 "export KRB5CCNAME='$KRB5CCNAME'"
        openssl=$(find_working openssl)
        if [ -n "$openssl" ]; then
          echo >&3 "KRB5OPENSSL='$openssl'"
          echo >&3 "KRB5BASE64='$($openssl enc -a -in $ccname)'"
        fi
      fi
    fi
  fi
  if [ -n "$DISPLAY" -a -n "$COOKIE" ]; then
    echo >&3 "xauth add $COOKIE"
  else
    echo >&3 "unset DISPLAY"
  fi
  if [ ! "$PROFILE_HOME" = "$HOME" ]; then
    echo >&3 "export SCREENRC=$PROFILE_HOME/.screenrc"
  fi
else
  exit 111
fi

echo >&3 ". ${PROFILE_HOME:-$HOME}/.bash_profile"
[ -f "$allusersprofile" ] && cat >&3 2>/dev/null "$allusersprofile"
[ -f "$userprofile" ] && cat >&3 2>/dev/null "$userprofile"
[ $chdir = 1 ] && echo >&3 2>/dev/null "cd - &>/dev/null"

exec 3>&-
dir=$(dirname "$0")
[ "$dir" = "." ] && dir="$PWD"
exec sudo -H -u "$user" "$dir/became"
exit 111