bash-setup-multi-user-environment

#!/bin/bash

# Share one account with serveral users but create their own environment
#
# Users are identified by their public key and cd'ed to their respective homes.
# Users have their own home and use their own .bashrc.

# Put this in your ~/.bashrc:
# eval $(~/bin/bash-setup-multi-user-environment)

set -e

function find_remote_host_via_ssh() {
    if [[ $SSH_CLIENT ]] ; then
        export REMOTE_HOST=${SSH_CLIENT%% *}
    fi
}

function find_login_via_ssh_key() {

    [[ $SSH_AUTH_SOCK ]] || return 0

    type -p ssh-add 1>/dev/null || return 0

    shopt -s nullglob
    local auth_files=(~/users/*/.ssh/authorized_keys)
    shopt -u nullglob

    [[ $auth_files ]] || return 0

    local agent_key
    while read agent_key ; do

        agent_key=${agent_key%%=*}

        [[ $agent_key ]] || continue;

        local auth_file
        for auth_file in ${auth_files[@]} ; do

            if grep -q "${agent_key}" $auth_file ; then
                REMOTE_USER=${auth_file%%/.ssh/authorized_keys};
                REMOTE_USER=${REMOTE_USER##$HOME/users/};
                return 0
            fi

        done

    done < <(ssh-add -L 2>/dev/null)

    return 0
}

function ask_for_login() {

    local NO_COLOR="\033[0m"
    local RED="\033[0;31m"

    local noagent
    ssh-add -L 1>/dev/null 2>/dev/null || noagent=1

    echo -en $RED

    if [[ $noagent ]] ; then
        return 0
    fi

    echo
    echo "Ups - do I know you?"
    echo
    echo -n "No - I'm new and "

    local sure
    until [[ $sure = "y" ]] ; do

        echo -n "I like to use this login, please: "
        read REMOTE_USER
        echo

        if [[ $REMOTE_USER =~ ^[a-z0-9_]+$ ]] ; then
            true
        elif [[ ! $REMOTE_USER ]] ; then
            REMOTE_USER=anonymous
        else
            echo "Invalid login - please try again."
            echo
            unset sure
            continue
        fi

        echo "Are sure you want to use $REMOTE_USER? (y/n)"
        read sure

    done

    echo -ne $NO_COLOR
}

function create_remote_home() {(
    set -e

    local NO_COLOR="\033[0m"
    local RED="\033[0;31m"

    local ssh_home=$REMOTE_HOME/.ssh
    local authorized_keys=$ssh_home/authorized_keys

    mkdir -p $REMOTE_HOME/{tmp,etc,bin,lib}
    mkdir -p $ssh_home

    if [[ $user = anonymous ]] ; then
        return 0
    fi

    set +e
    ssh-add -L >> $authorized_keys 2>/dev/null
    set -e

    echo -ne $RED

    if [[ $REMOTE_USER = anonymous ]] ; then
        echo
        echo "To get a personalized home directory please activate"
        echo "   your ssh-agent with key forwarding!"
        echo
        echo "If you want to be someone specific remove your ssh public key from:"
        echo "   $REMOTE_HOME/.ssh/authorized_keys"
        echo "   and login again."
        echo
        echo "If you are a script please make sure you are not running"
        echo "   bash interactively to avoid this screen."
        echo
        echo "For now you will be known as anonymous."
    fi

    echo
    echo "Please keep the official home ($HOME) clean."
    echo "Store your own files in $REMOTE_HOME."
    echo "Thank you!"
    echo
    echo "   Use 'cdh' to go to your personal home at $REMOTE_HOME."
    echo "   Use 'cdt' to go to your personal tmp at $REMOTE_HOME/tmp."
    echo
    echo "Have fun!"
    echo
    echo -ne $NO_COLOR
)}

# do not allow ctrl-c
trap '' INT

find_remote_host_via_ssh
find_login_via_ssh_key

if [[ ! $REMOTE_USER ]] ; then
    ask_for_login >&2
    new_user=1
fi

if [[ ! $REMOTE_USER ]] ; then
    REMOTE_USER=anonymous
    new_user=1
fi

export REMOTE_USER
export REMOTE_HOME="$HOME/users/$REMOTE_USER"
export REMOTE_BASHRC="$REMOTE_HOME/.bashrc"

if [[ $new_user ]] ; then
    create_remote_home >&2
fi

# needs trailing ; because eval joins the lines
cat <<-EOF
    export REMOTE_USER=$REMOTE_USER;
    export REMOTE_HOME=$REMOTE_HOME;
    export REMOTE_BASHRC=$REMOTE_BASHRC;
    alias cdh="cd $REMOTE_HOME";
    alias cdt="cd $REMOTE_HOME/tmp";
    alias ssh="ssh -A";
    cd $REMOTE_HOME;
EOF

if [[ -e $REMOTE_BASHRC ]] ; then
    if [[ $REMOTE_USER != anonymous ]] ; then
        echo "source $REMOTE_BASHRC"
    fi
fi