# kdo is a shell function for interacting with multiple Kerberos
# credential caches.
#
# To use kdo, add this snippet to your .bashrc or .bashrc.mine file.
#
# To run a command with a different set of credentials from your
# default, run
#
#     kdo <principal> <command>
#
# e.g.,
#
#     kdo broder/root aklog
#
# If you lack credentials for the specified principal, you'll be
# prompted for the password.
#
# If kdo needs to acquire tickets, it will pass the value of
# ${kdo_args[@]} to kinit. I use this to get tickets that last for 15
# minutes, that are renewable for 60 minutes, and aren't forwardable.
#
# To add kdo support for a new platform, you need to provide an
# interface to multiple credential caches by defining two functions:
#
#  - kcaches::
#      Print one line per current credential cache of the form "<KRB5CCNAME> <PRINCIPAL>" 
#  - knewcache::
#      Without changing the current credentials cache, get credentials
#      for the principal in $1, passing the remaining arguments to
#      kinit.
#      knewcache should set the variable cache with the KRB5CCNAME
#      value for the newly created credential cache
#
# Also included is krootssh, a wrapper around ssh for using your
# root-instance tickets with ssh. It ensures that your tickets don't
# get accidentally forwarded, on the off chance that you have
# forwardable tickets.

# CONFIGURATION
kdo_args=(-l15m -r60m -F)

# CC interface for OS X
if [ "Darwin" = "$(uname)" ]; then
    kcaches () {
        klist -A | awk '/^Kerberos 5 ticket cache:/ {cache = $5; princline=NR+1} NR==princline {print substr(cache, 2, length(cache)-2), $3}'
    }

    knewcache () {
        princ="$1"; shift
        local oldcache="$(klist | grep 'Kerberos 5 ticket cache' | cut -f 2 -d "'")"
        kinit "$@" "$princ" || return 1
        cache="$(kfindcache "$princ")"
        # On OS X, kinit will switch your default credential cache to
        # that of the newly acquired tickets, so switch back if we can
        if [ -z "$oldcache" ]; then
            echo "W: Tickets for $princ are now in your default credential cache" >&2
        else
            kswitch -c "$oldcache"
        fi
    }
fi

# If kcaches and knewcache have been defined for this platform, then
# setup kdo. Otherwise, add a helpful error.
if hash kcaches &>/dev/null && hash knewcache &>/dev/null; then
    kfindcache () {
        kcaches | fgrep "$1" | awk '{print $1}'
    }

    kdo () {
        local princ="$1"; shift
        local cache="$(kfindcache "$princ")"
        # If the cache that we want to use has expired tickets, then
        # destroy that cache so we don't try to use it again and clear
        # $cache so that we'll revert to acquiring a new set of
        # tickets
        if [ -n "$cache" ] && ! klist -s "$cache"; then
            KRB5CCNAME="$cache" kdestroy
            cache=""
        fi
        if [ -z "$cache" ]; then
            knewcache "$princ" "${kdo_args[@]}" || return 1
        fi
        echo "I: Running $1 with cache $cache (for principal $princ)" >&2
        KRB5CCNAME="$cache" "$@"
    }
    _kdo () {
        local cur
        COMPREPLY=()
        cur="${COMP_WORDS[COMP_CWORD]}"
        opts="$(kcaches | awk '{ print $2 }')"
        case $COMP_CWORD in
            1)
                COMPREPLY=($(compgen -W "${opts}" -- "${cur}"))
                ;;
            2)
                COMPREPLY=($(compgen -c -- "${cur}"))
        esac
    }
    complete -o bashdefault -F _kdo kdo

    krootssh () {
        kdo ${ATHENA_USER:-$USER}/root@ATHENA.MIT.EDU ssh -o GSSAPIDelegateCredentials=no "$@"
    }
else
    kdo () {
        echo "kdo has not been ported to this platform yet." >&2
        return 1
    }

    krootssh () {
        echo "kdo has not been ported to this plastform yet." >&2
        return 1
    }
fi