AD Plugin UID calculation from ObjectGUID

convert.sh

#!/bin/bash

#
# Author:   Calum Hunter
# Date:     28/11/2016
# Version:  1.0
# Purpose:  To generate a Mac UID from the objectGUID attribute
#           (GeneratedUID) in AD. 
#           This uses the same method that the Apple
#           AD Plugin uses
#

## Start by loading up our ldap query variables
SVC_ACCOUNT_NAME="Username"
SVC_ACCOUNT_PASS="Password"
DOMAIN="my.domain"
LDAP_SERVER="dc.my.domain:389"
SEARCH_BASE="CN=John\, Smith,OU=Users,DC=MY,DC=DOMAIN"

DECODE_BASE64(){
    # This function takes the encoded output from ldapsearch and decodes it 
    # It then needs to be "hex-dumped" in order to get it into regular text
    # So that we can work with it
    OBJECT_ID="$1"
    BASE64_DECODED=$(echo $OBJECT_ID | base64 -D)
    G=($(echo ${BASE64_DECODED} | hexdump -e '16/1 " %02X"'))
    OBJECTGUID="${G[3]}${G[2]}${G[1]}${G[0]}-${G[5]}${G[4]}-${G[7]}${G[6]}-${G[8]}${G[9]}-${G[10]}${G[11]}${G[12]}${G[13]}${G[14]}${G[15]}"
}

# Search LDAP for our user account
RESULT=$(ldapsearch -LLL -H ldap://$LDAP_SERVER -o ldif-wrap=no -x -D ${SVC_ACCOUNT_NAME}@$DOMAIN -w ${SVC_ACCOUNT_PASS} -b "${SEARCH_BASE}" \
-s sub -a always "(objectClass=user)" "objectGUID")

# Get our user DN and objectGUID from the result above.
USER_DN=$(echo "$RESULT" | grep "dn:")
USER_GUID_BASE64=$(echo "$RESULT" | awk -F "::" '/objectGUID/ {print $2}')

# Get our GeneratedUID from LDAPSEARCH by decoding and hex dumping it
DECODE_BASE64 "$USER_GUID_BASE64"

# Now lets get the first 32 bits of our GUID
GUID_32=${OBJECTGUID:0:8}
# Now convert this to decimal
GUID_32_DEC=$(echo "ibase=16; $GUID_32" | bc)

# Check if this is greater than the largest decimal figure allowed for a mac UID (32Bit Integer)
if [ $GUID_32_DEC -gt 2147483647 ]; then
    # Get the first character of our 32bit GUID
    FIRST_CHAR=${GUID_32:0:1}
    # Use the below table to replace the first character with number it represents. ie: A=2
    case $FIRST_CHAR in
        A)
            NUMBER=2 ;;
        B)
            NUMBER=3 ;;
        C)
            NUMBER=4 ;;
        D)
            NUMBER=5 ;;
        E)
            NUMBER=6 ;;
        F)
            NUMBER=7 ;;
        9)
            NUMBER=1 ;;
        8)
            NUMBER=0 ;;
        *)
    esac
    # Now lets replace the first character with our new number
    A=$(echo $GUID_32 | cut -c2-)
    NEW_32_GUID="${NUMBER}${A}"
    GUID_32_DEC=$(echo "ibase=16; $NEW_32_GUID" | bc)
fi

# Echo our output
echo "User: $(echo $USER_DN | awk -F "dn:" '{print $2}')"
echo "ObjectGUID: $OBJECTGUID"
echo "Mac UID: $GUID_32_DEC"