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% Copyright (c) 2004 by Nick Urbanik <nicku(at)nicku.org>.
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\title{\blue{}Network Directories and their Structure}
\subtitle{Lightweight Directory Access Protocol (LDAP)}
%% \author{Nick Urbanik \texttt{<nicku\at{}nicku.org>}\\
%%   \footnotesize{}Copyright Conditions: Open Publication License (see
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\author{Nick Urbanik \texttt{<nicku\at{}nicku.org>}\\
  \footnotesize{}Copyright Conditions: Open Publication License (see
  \url{http://www.opencontent.org/openpub/})\\
\institution{A computing department}}%
%\footnotesize{}Copyright Conditions: GNU FDL (see
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\slideCaption{SNM --- LDAP Directories --- ver. \RCSRevision}
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\begin{document}
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\maketitle

\tsection{Introduction to Directories}

\begin{slide}{Network Directories and their Structure}
  \begin{center}
    Lightweight Directory Access Protocol (\LDAP)
  \end{center}
  \begin{center}
    Organising accounts in a large network
  \end{center}
  \begin{center}
    Reference book: \emph{Understanding and Deploying LDAP Directory
      Services}, Second Edition, Timothy Howes, Mark Smith and Gordon
    Good, Macmillan, 2003.
  \end{center}
  \begin{center}
    Our library: TK 5105.595 .H69 2003
  \end{center}
  \begin{center}
    (also see references at the end of slides)
  \end{center}
\end{slide}

%% \begin{slide}{Network Design}
%%   \begin{itemize}
%%   \item As in our teaching plan, Network Design is our next topic.
%%   \item I will include some topics from:
%%    \begin{itemize}
%%    \item Designing a directory infrastructure
%%    \item Automating the naming and configuration of network: more
%%      advanced topics in DHCP and DNS
%%    \item Designing the routing and switching infrastructure
%%    \end{itemize}
%%   \item This first topic is directory infrastructure
%%   \end{itemize}
%% \end{slide}

\begin{slide}{Account Information}
  \begin{itemize}
  \item The computer uses numbers to refer to users and groups
  \item Humans prefer to use names (like nicku)
  \item When you create files in your shared network drive, the client
    must access them using the same numbers
  \item The user ID numbers and group ID numbers must be the same on
    all computers
  \item Otherwise won't be able to read own files!
  \end{itemize}
\end{slide}

\begin{slide}{Network Accounts}
\begin{itemize}
\item
\begin{alltt}\tiny
$ \textbf{ls -ln file}
-rw-rw----    1 500      500          2057 Nov  1  2000 file
\end{alltt}%$
\item Now nicku with user \ID number 500 and group \ID 500 can read
  and write this file
\item \ldots{}But nicku with user \ID number 2270 and group \ID number
  2270 cannot access the file at all:
\begin{alltt}\tiny
$ \textbf{id}
uid=2270(nicku) gid=2270(nicku) groups=2270(nicku),14171(staff)
\end{alltt}%$
\end{itemize}
\end{slide}

\begin{slide}{Network Accounts --- 2}
  \begin{itemize}
  \item The user \ID numbers and group \ID numbers on files on a
    network drive are fixed
  \item The user \ID numbers should remain unchanged for all users who
    read/write the network drive.
  \end{itemize}
\end{slide}

\begin{slide}{Methods of achieving this}
  \begin{itemize}
  \item Have a \emphcolour{directory server} of some kind
  \item The directory server associates a fixed user \ID number with
    each login \ID
  \item \ldots{}and a fixed group \ID number for each group \ID
  \item On \NT, these are called \acro{SID}{}s (security \ID{}s)
\end{itemize}
\end{slide}

\begin{slide}{Directory systems for authentication}
  \begin{itemize}
  \item Proprietary:
    \begin{itemize}
    \item Novell Directory Services (\acro{NDS})
    \item Microsoft Active Directory (M? \acro{AD})
    \item \NT 4 domain
    \item \NIS+ (Network Information System plus)
    \item \NIS
    \end{itemize}
  \item Open protocols:
    \begin{itemize}
    \item \LDAP
    \item Hessiod
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Proprietary application directories}
  \begin{itemize}
  \item Application-specific directories:
    \begin{itemize}
    \item Lotus Notes
    \item cc:Mail
    \item Microsoft Exchange
    \item Novell GroupWise
    \end{itemize}
  \item These directories come bundled with, or, embedded into an
    application such as email.
  \item If add another such application, must manage one more
    directory (``$N + 1$ directory problem'')
  \item If add another user, must add to all the directories.
\end{itemize}
\end{slide}

\begin{slide}{Problem with proprietary directories}
  \begin{itemize}
  \item Need put the same user into many different directories
  \item Need maintain $N$ times the number of user accounts, where $N$
    is the number of directories.
  \item This is just too much work.
  \item The accounts get out of sync.
  \end{itemize}
\end{slide}

\begin{slide}{Why not buy Microsoft AD?}
\label{sld:why-not-microsoft-ad}
  \begin{itemize}\scriptsize
  \item Microsoft leverage their monopoly on the desktop to ``embrace
    and extend'' free software written by others
  \item Example:
    \begin{itemize}
    \item Kerberos is a ``Network Authentication Service'', an
      \acro{IETF} standard (see \RFC 1510)
    \item Kerberos is written by cooperating programmers round the
      world
    \item Microsoft took Kerberos, and modified the protocol very
      slightly (they classified this change as a ``trade secret'')
    \item So that \MS destops can use \MS Kerberos servers, but not
      non-MS Kerberos servers.
    \end{itemize}
  \item Although \MS claims to support standards, \MS solutions are
    highly proprietary
  \item Designed to lock the user into an all-\MS solution.
  \item Could be an expensive and insecure mistake.
\end{itemize}
\end{slide}

\tsection{LDAP}

\begin{slide}{\LDAP --- Why?}
  \begin{itemize}
  \item Non-proprietary, IETF standard
    \begin{itemize}
    \item No vendor lock-in
    \item Use standard software components
    \end{itemize}
  \item Supports authorisation as well as authentication
    \begin{itemize}
    \item E.g., access if ``staff, or year 3, group W, CSA student''
    \end{itemize}
  \item Very general purpose: use for email, system authentication,
    application authentication, \ldots
  \item Reasonably secure
  \item Robust
  \item Extensible
  \item Good open source implementation available at
    \url{http://www.OpenLDAP.org/}
\end{itemize}
\end{slide}

\begin{slide}{\LDAP Terminology}
  \begin{itemize}
  \item \LDAP model is \emphcolour{hierarchical}, i.e., tree-structured
  \item Each object in a directory is an \emphcolour{entry}
  \item Each individual item in an entry is an \emphcolour{attribute}
  \item Each entry has a unique full name called its
    \emphcolour{distinguished name} or \emphcolour{dn}
  \item Each entry has a short name that is unique under its parent,
    called its \emphcolour{relative distinguished name}, or \emphcolour{rdn}.
  \item The organisation of names in the directory is called the
    \emphcolour{namespace}
  \item An important initial task is \emphcolour{namespace design}
\end{itemize}
\end{slide}

\begin{slide}{What is \LDAP?}
  \begin{itemize}
  \item The \LDAP \emphcolour{protocol}, a standard Internet protocol
  \item Four \emphcolour{models}:
    \begin{multicols}{2}
      \begin{itemize}
      \item \emphcolour{information~model}---what you can put in directory
      \item \emphcolour{naming~model}---how name directory data
      \item \emphcolour{functional~model}---what you can do with data
      \item \emphcolour{security~model}---no unauthorised access
      \end{itemize}
      %\setcounter{unbalance}{-1}
    \end{multicols}
  \item \LDAP Data Interchange Format ({\red\LDIF}), a standard text format
    for representing directory data
  \item \LDAP \emphcolour{server software}
  \item \emphcolour{command line utilities} (\texttt{ldapsearch},
    \texttt{ldapmodify},\,\ldots)
  \item {\mbox{}\red\LDAP \API}
  \end{itemize}
\end{slide}

\begin{slide}{The \LDAP Protocol}
  \begin{itemize}
  \item \LDAP is a \emphcolour{message-based} protocol
    \begin{itemize}
    \item client sends one or more requests to server, one message per
      request
      \begin{itemize}
      \item Each message has its own \emphcolour{message ID}
      \end{itemize}
    \item server replies with one or more replies.  Each reply has
      message \ID matching that of request.
    \item Can send  several messages at once; results can be out of
      order, no problem
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Simple Search Examples}
  \begin{center}
    \includegraphics[width=0.7\slideWidth]{single-request}
  \end{center}
  \vspace*{-\baselineskip}
  \begin{itemize}
  \item Here a client gets one single entry from the directory
  \end{itemize}
  \begin{center}
    \includegraphics[width=0.7\slideWidth]{multiple-response}
  \end{center}
  \vspace*{-\baselineskip}
  \begin{itemize}
  \item A client gets multiple responses from the directory
  \end{itemize}
\end{slide}

\begin{slide}{Multiple Simultaneous Requests}
   \begin{center}
    \includegraphics[width=0.7\slideWidth]{multiple-request}
  \end{center}
  \begin{itemize}
  \item A client sends multiple requests to the directory
  \item Note that each request has its own \texttt{msgid}
  \item Responses may come out of order (see last two result codes);
    that's okay.
    \begin{itemize}
    \item These details are hidden from programmer by the \acro{SDK}
      (software development kit)
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP Protocol Operations}
  \begin{itemize}
  \item Interrogation operations: \texttt{search}, \texttt{compare}
  \item Update operations: \texttt{add}, \texttt{delete},
    \texttt{modify}, \texttt{modify~DN} (rename)
  \item Authentication and control operations: \texttt{bind},
    \texttt{unbind}, \texttt{abandon}
    \begin{description}
    \item[\texttt{bind}] operation allows a client to identify itself
      sending identity and authentication credentials
    \item[\texttt{unbind}] operation allows client to terminate
    session
  \item[\texttt{abandon}] operation allows a client to tell the server
    it does not need the results of an operation it had requested earlier
    \end{description}
  \end{itemize}
\end{slide}

\begin{slide}{Typical \LDAP Exchange}
  \label{sld:typical-ldap-exchange}
   \begin{center}
    \includegraphics[width=0.7\slideWidth]{typical-ldap-request}
  \end{center}
  \begin{itemize}
  \item The \emphcolour{bind operation} provides a
    \emphcolour{distinguished name} (\DN) and other credentials to
    authenticate against the directory
  \item The \emphcolour{unbind operation} is a request to disconnect
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP Encoding: \BER}
  \begin{itemize}
  \item The \LDAP protocol uses the \emphcolour{Basic Encoding Rules},
    \BER to encode various data types in a platform independent way
  \item These are the same rules as used in \SNMP
  \item Therefore it is not a simple text-based protocol, like
    \acro{HTTP} or \acro{SMTP}.
  \end{itemize}
\end{slide}

\tsection{LDAP Operations}

\begin{slide}{\LDAP Search Operation}
  \label{sld:ldap-search-operation}
  \begin{itemize}
  \item Used to search for entries and retrieve them
    \begin{itemize}
    \item This is the only way to read the directory
    \end{itemize}
  \item Takes eight parameters, including:
    \begin{itemize}
    \item \DN of base object for search --- see slide~\S\pageref{sld:search-scope}
    \item search scope --- see slide~\S\pageref{sld:search-scope}
    \item search filter --- see slide~\S\pageref{sld:filters}
    \item list of attributes to return
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Search Scope}
  \label{sld:search-scope}
  \newcommand*{\scale}{0.27}
  \begin{center}
    \begin{minipage}[t]{0.3\slideWidth}
      \begin{tabularx}{\linewidth}{X}
        \includegraphics[scale=\scale]{scope-base}\\
        Search scope = \emphcolour{base}
      \end{tabularx}
    \end{minipage}%
    \hspace{1ex}%
    \begin{minipage}[t]{0.3\slideWidth}
      \begin{tabularx}{\linewidth}{X}
        \includegraphics[scale=\scale]{scope-one}\\
        Search scope = \emphcolour{one}
      \end{tabularx}
    \end{minipage}%
    \hspace{1ex}%
    \begin{minipage}[t]{0.3\slideWidth}
      \begin{tabularx}{\linewidth}{X}
      \includegraphics[scale=\scale]{scope-sub}\\
        Search scope = \emphcolour{subtree}
      \end{tabularx}
    \end{minipage}
  \end{center}
  \begin{itemize}
  \item In each case, the search base is \path{ou=People,dc=ict,dc=edu,dc=hk}
  \end{itemize}
\end{slide}

\begin{slide}{The Compare Operation}
  \label{sld:compare-operation}
  \begin{itemize}
  \item Not very useful
  \item I use it for determining if a user belongs to a particular
    group
  \item main difference from search:
    \begin{itemize}
    \item If compare on an attribute that does not exist in a
      particular entry, returns code indicating this
    \item If search for an attribute that does not exist in a
      particular entry, then get nothing returned.
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Add Operation}
  \label{sld:add-operation}
  \begin{itemize}
  \item Creates a new entry, given two parameters:
    \begin{itemize}
    \item \DN of new entry
    \item list of attributes and their values to put in the new entry
    \end{itemize}
  \item Will succeed if and only if:
    \begin{itemize}
    \item parent of new entry exists
    \item no entry of same name exists
    \item new entry matches requirements of schemas
    \item access control allows operation
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Delete Operation}
  \label{sld:delete-operation}
  \begin{itemize}
  \item Deletes an entry
  \item Takes \DN of entry to delete
  \item Succeeds if:
    \begin{itemize}
    \item entry exists
    \item entry has no children
    \item access control allows operation
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Modify \DN (Rename) Operation}
  \label{sld:modify-dn-operation}
  \begin{itemize}
  \item Used to rename or move an entry from one place in tree to
    another
  \item Has four parameters:
    \begin{itemize}
    \item Old \DN
    \item New \DN
    \item New \RDN for entry
    \item optional flag indicating whether to delete the old \RDN
      attribute from the entry
    \end{itemize}
  \item Succeeds if:
    \begin{itemize}
    \item entry exists
    \item new name not already used
    \item access control allows operation
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Modify Operation}
  \label{sld:modify-operation}
  \begin{itemize}
  \item Allows updating existing entry
  \item Can add, delete or replace attributes
  \item Can modify many attributes in one modify operation
  \item Succeeds if and only if:
    \begin{itemize}
    \item entry exists
    \item all attribute modifications must succeed
    \item resulting entry obeys schemas
    \item access control permits modification
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Bind Operation}
  \label{sld:bind-operation}
  \begin{itemize}
  \item authenticates client to the directory
  \item Three bind types:
    \begin{itemize}
    \item \emphcolour{simple bind}, where send \DN and password in
      clear text to server
      \begin{itemize}
      \item Need to use \TLS to encrypt communication in this case
      %\item with \texttt{ldapsearch} utility, specify using option \texttt{-x}
      \end{itemize}
    \item {\mbox{}\red\acro{SASL} bind}
      \begin{itemize}
      \item \acro{SASL} = Simple Authentication and Security Layer
      \item A standard protocol independent way of negotiating and
        performing authentication
      \end{itemize}
    \item \emphcolour{anonymous bind}, where send \DN but no passwords
    \end{itemize}
  \item Client can bind, perform operations, bind again, and perform
    other operations
  \end{itemize}
\end{slide}

\tsection{Utilities and LDIF}

\begin{slide}{Command Line Utilities}
  \label{sld:command-line-utilities}
  \begin{itemize}
  \item With Open\LDAP, the main utilities (in RH Linux, in the
    package \texttt{openldap-clients}) are:
    \begin{description}
    \item[\texttt{ldapsearch}] Query directory
    \item[\texttt{ldapmodify}] Perform the modify operation on an entry --- see
    \S\pageref{sld:ldapmodify-ldif}
    \item[\texttt{ldapdelete}] Delete an entry
    \item[\texttt{ldapadd}] Add an entry
    \item[\texttt{ldapmodrdn}] Rename an entry
    \item[\texttt{ldapcompare}] Compare operation
    \item[\texttt{ldappasswd}] Change \LDAP password using LDAPv3 Password
      Modify (RFC 3062) extended operation
    \end{description}
  \item Each one has a detailed \texttt{man} page
  \end{itemize}
\end{slide}

\begin{slide}{Common Parameters}
  \label{sld:command-line-utilities-common-pcarameters}
  \begin{itemize}
  \item All commands use the \acro{SASL} (Simple Authentication and
    Security Layer) protocol by default
    \begin{itemize}
    \item But won't work here:
    \item \ldots\,we use simple authentication here (we send plain
      text passwords over link encrypted with Transport Layer
      Security i.e., \TLS or \SSL)
    \end{itemize}
  \item ``\texttt{-x}'' use simple authentication
    instead of \acro{SASL}
  \item specify hostname of server with \texttt{-h}, e.g.,
    \texttt{-h~ldap.vtc.edu.hk}
  \item Specify a \DN to bind with using \texttt{-D} (see
    \S\pageref{sld:ldapmodify-ldif})
  \item Specify a password on command line with
    \texttt{-w~\meta{password}}  or interactively prompt using
    \texttt{-W}
    \begin{itemize}
    \item See \S\pageref{sld:ldapmodify-ldif},
      \S\pageref{sld:using-ldapsearch-3-bind} for examples
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{\texttt{ldapsearch}}
  \label{sld:ldapsearch}
  \begin{itemize}
  \item Specify \emphcolour{base} of search with
  \texttt{-b~\meta{DN~of~search~base}}
    \begin{itemize}
    \item Default can be specified as a line in
    \path{/etc/openldap/ldap.conf}, e.g.,
\begin{verbatim}
BASE dc=tyict,dc=vtc,dc=edu,dc=hk
HOST ldap.tyict.vtc.edu.hk
\end{verbatim}
    \end{itemize}
  \item Specify \emphcolour{scope} of search with
    \texttt{-s~[base|one|sub]}
    \begin{itemize}
    \item Default scope is subtree scope
    \end{itemize}
  \item See \S\pageref{sld:using-ldapsearch-with-filter} for more examples.
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP Data Interchange Format \LDIF}
\label{sld:ldif-1}
  \begin{itemize}
  \item A standard defined in \RFC 2849
  \item Used to import, export directory data in a standard way
    \begin{itemize}
    \item A bit like how all spreadsheets understand tab-delimited
    text files
    \end{itemize}
  \item Can also specify update operations to directory entries.
  \end{itemize}
\end{slide}

\begin{slide}{Example \LDIF}
\label{sld:example-ldif}
\ptsize{10}\footnotesize
\begin{verbatim}
dn: uid=nicku,ou=People,dc=ict,dc=vtc,dc=edu,dc=hk
uid: nicku
cn: Nick Urbanik
givenName: Nick
sn: Urbanik
mail: nicku@nicku.org
objectClass: person
objectClass: organizationalPerson
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: top
loginShell: /bin/sh
uidNumber: 1000
gidNumber: 1000
homeDirectory: /opt/nicku
mail: nicku@nickpc.tyict.vtc.edu.hk
description: Interested in free software
\end{verbatim}
\end{slide}

\begin{slide}{Update Operation in \LDIF}
\label{sld:ldapmodify-ldif}
\ptsize{10}
\begin{alltt}\footnotesize
$ \textbf{cat /tmp/update-nick.ldif}
dn: uid=nicku,ou=People,dc=ict,dc=vtc,dc=edu,dc=hk
changetype: modify
replace: mail
mail: nicku@nicku.org
-
add: title
title: Lecturer in SNM
-
add: jpegPhoto
jpegPhoto:< file://tmp/penguin.jpg
-
delete: description
-
$ \textbf{ldapmodify -x -D 'uid=nicku,ou=People,dc=ict,dc=vtc,dc=edu,dc=hk' \bs
-W -f /tmp/update-nick.ldif}
Enter LDAP password:
modifying entry "uid=nicku,ou=People,dc=ict,dc=vtc,dc=edu,dc=hk"
\end{alltt}  
\end{slide}

\tsection{Schemas}

\begin{slide}{\LDAP Schemas}
  \begin{itemize}
  \item The directory has a set of rules that determine the allowed
    objectclasses and attributes
  \item Called the \emphcolour{schemas}
  \item Can be defined in
    \begin{itemize}
    \item ASN.1, or
    \item University of Michigan style, or
    \item \LDAP{}v3 style
    \end{itemize}
  \item Each object, and its syntax, are both defined using \OID{}s,
    as in \SNMP.
  \end{itemize}
\end{slide}  

\begin{slide}{Attributes --- Defined in Schema}
  \begin{itemize}
  \item For each attribute, schema defines:
    \begin{itemize}
    \item Name
    \item Description
    \item Permitted compare operations
    \item Syntax (i.e., data type).
    \end{itemize}
  \item \LDAP server ensures that all added data matches the schema
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP objectClass --- 1}
  \begin{itemize}
  \item Each attribute belongs to one or more \textbf{objectClass}es
  \item objectClasses are defined in schemas
  \item Defines what attributes \emphcolour{must}, or \emphcolour{may} be
    present in an entry
  \item objectClass definition includes:
    \begin{itemize}
    \item Name of objectClass
    \item What subclass this is derived from
    \item The type of objectClass: \emphcolour{structural},
      \emphcolour{auxiliary} or \emphcolour{abstract}
    \item Description
    \item List of \emphcolour{required} attributes
    \item List of \emphcolour{allowed} attributes
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Object Class and Attributes}
  \begin{itemize}
  \item The entry can use all the attributes allowed in all the
    objectClasses.
    \begin{itemize}
    \item See in slide~\S\pageref{sld:namespace-of-atributes} how
      \LDAP attributes differ from attributes in, say, a Java class
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP Object Class Inheritance}
  \begin{itemize}
  \item \LDAP implements a limited form of object oriented inheritance
  \item One entry may contain many objectClasses
    \begin{itemize}
    \item We say, ``an entry belongs to many classes''
    \end{itemize}
  %\item Single, not multiple inheritance---see page 272,
    % Understanding and Deploying LDAP, second edition, but if you
    % look in cosine.schema for the definition of pilotOrganization
    % which inherits from both organization and organizationalUnit.  Try
    % $ grep -i 'sup \+(' /etc/openldap/schema/*
  \item Cannot override any schema rules defined in superior class
  \item Example: top~\generalises\ person~\generalises\
    organizationalPerson~\generalises\ inetOrgPerson
    \begin{itemize}
    \item In \texttt{/etc/openldap/schema}, \texttt{core.schema}
      defines person, organizationalPerson;
      \texttt{inetorgperson.schema} defines inetOrgPerson
    \end{itemize}
  \item A class derived from another class includes the attributes of
    its superior class(es)
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP Object Class Type}
  \begin{itemize}
  \item objectClass has a type: \emphcolour{structural},
    \emphcolour{auxiliary}, or \emphcolour{abstract}
  \item Default is \emphcolour{structural}
  \item \textbf{Structural} is for the fundamental, basic aspects of
    the object, e.g., \textbf{person}, \textbf{posixGroup},
    \textbf{device}.
  \item \textbf{Auxiliary} classes place no restrictions on where an
    entry is stored, and are used to add more attributes to structural
    classes.
  \item \textbf{Abstract} classes are not usually created by users;
    the class \textbf{top} and \textbf{alias} are abstract.
  \end{itemize}
\end{slide}

\begin{slide}{Structural Classes}
  \begin{itemize}
  \item Rule of \LDAP standards: if an entry belongs to more than one 
    \emphcolour{structural} class, they must be related by inheritance
    \begin{itemize}
    \item Open\LDAP 2.0.x does not implement this restriction, but
      Open\LDAP 2.1.x and later versions (including 2.2.x) do.
    \end{itemize}
  \item To get around this, can either:
    \begin{itemize}
    \item Implement a new objectClass that is of type auxiliary that
      allows the attributes you require---see
      \url{http://www.openldap.org/faq/data/cache/883.html}
  \item Implement a new objectClass that inherits from both unrelated
    structural classes and use that---See
    \url{http://www.openldap.org/faq/data/cache/807.html} .
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Entries: Selecting Object Class Types}
  \begin{itemize}
  \item Entries contain one or more \emphcolour{objectClass}es
  \item Choose the attributes you need
  \item Select the objectClasses that provide these attributes
  \item Add the objectClass to your entry.
  \end{itemize}
\end{slide}

\begin{slide}{Rules for \LDAP Entries}
  \begin{itemize}
  \item Each entry must be a member of the objectClass
    \texttt{\red{}top}
  \item Each entry must be a member of the objectClass that
    provides the attributes
  \item Exactly {\green{}one objectClass should be structural}, the
    rest auxiliary (or abstract)
    \begin{itemize}
    \item An entry may belong to more than one structural class if all
      structural classes are {\green{}related by inheritance}
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Namespace of attributes}
  \label{sld:namespace-of-atributes}
  \begin{itemize}
  \item There is {\green{}only one namespace for attributes}
  \item The definition of the attribute \texttt{cn} (common name) is
    the same for all objectClasses that support the \texttt{cn}
    attribute.
  \end{itemize}
\end{slide}

\begin{slide}{Example objectTypes}
  \begin{itemize}
  \item Here is the definition for person from core.schema:
\begin{verbatim}
objectclass ( 2.5.6.6 NAME 'person'
  SUP top STRUCTURAL
  MUST ( sn $ cn )
  MAY ( userPassword $ telephoneNumber $
        seeAlso $ description ) )
\end{verbatim}
  \item This says a person entry \emphcolour{must} contain:
    \begin{itemize}
    \item a surname (\texttt{sn}) and
    \item common name (\texttt{cn}),
    \end{itemize}
  \item and \emphcolour{may} contain a userPassword, a
    telephoneNumber, a description, and a reference to another \LDAP
    entry.
\end{itemize}
\end{slide}

\begin{slide}{Want to support network login}
  \begin{itemize}
  \item Does the objectClass person provide what is needed for network
    login?
  \item For network accounts, need replace (at minimum):
    \vspace*{-1.5ex}
    \begin{multicols}{2}
      \begin{itemize}
      \item \texttt{/etc/passwd}
      \item \texttt{/etc/shadow}
      \item \texttt{/etc/group}
      \end{itemize}
    \end{multicols}
    \vspace*{-1.5ex}
\item So in addition to attributes of person, need:
    \vspace*{-1.5ex}
    \begin{multicols}{2}
      \begin{itemize}
      \item User \ID name (log in name)
      \item User \ID number
      \item Primary group \ID number
      \item Gecos information (fifth field of \texttt{/etc/passwd})
      \item Home directory
      \item Login shell
      \end{itemize}
    \end{multicols}
    \vspace*{-2ex}
  \item Also the password aging information from \texttt{/etc/shadow}
\end{itemize}
\end{slide}

\begin{slide}{Supporting network login}
  \begin{itemize}
  \item Use the existing objectClass \texttt{posixAccount}:
{\footnotesize
\begin{verbatim}
objectclass ( 1.3.6.1.1.1.2.0 NAME 'posixAccount'
  SUP top AUXILIARY
  DESC 'Abstraction of an account with POSIX
        attributes'
  MUST ( cn $ uid $ uidNumber $ gidNumber $
         homeDirectory )
  MAY ( userPassword $ loginShell $ gecos $
        description ) )
\end{verbatim}%$
}
  \item Provides fields from \texttt{/etc/passwd}
  \end{itemize}
\end{slide}

\begin{slide}{Authorisation as well as authentication}
  \begin{itemize}
  \item Suppose you have an online web-based quiz, want only staff,
    or year 3, group W, CSA student to be allowed to log in.
  \item For this to work:
  \item Each person entry has attributes including:
    \begin{itemize}
    \item \texttt{Course}, e.g., 41300
    \item \texttt{classCode}, e.g., W
    \item \texttt{Year}, e.g., 3
    \item \texttt{acType}, e.g., STU or STF
    \end{itemize}
  \end{itemize}
\end{slide}

\tsection{LDAP Filters \& URLs}

\begin{slide}{\LDAP filters}
  \label{sld:filters}
\begin{itemize}
\item \LDAP provides a standard method for selecting authenticated
  users who match authorisation criteria
\item The filter to select staff or students in year 3, CSA, group W
  is:
\begin{verbatim}
(|(acType=STF)(&(year=3)(course=41300)
(classcode=W)))
\end{verbatim}
(\small This line is wrapped to fit on the slide, but normally given
on one line)
\item All filters are enclosed in parentheses
\item Filters can be combined with OR `\textbar', AND `\texttt{\&}' 
\end{itemize}
\end{slide}


\begin{slide}{RFC 2254 --- 1}
Find this in \texttt{/usr/share/doc/openldap-2.0.27/rfc/rfc2254.txt}
\begin{verbatim}
filter     = "(" filtercomp ")"
filtercomp = and / or / not / item
and        = "&" filterlist
or         = "|" filterlist
not        = "!" filter
filterlist = 1*filter
item       = simple / present / substring
simple     = attr filtertype value
filtertype = equal / approx / greater / less
equal      = "="
approx     = "~="
greater    = ">="
less       = "<="
\end{verbatim}
\end{slide}

\begin{slide}{RFC 2254 --- 2}
\begin{verbatim}
present    = attr "=*"
substring  = attr "=" [initial] any [final]
initial    = value
any        = "*" *(value "*")
final      = value
attr       = AttributeDescription from Section 4.1.5 of [1]
value      = AttributeValue from Section 4.1.6 of [1]
[1] is RFC 2251.
Grammar is defined in RFC 822
\end{verbatim}
\end{slide}

\begin{slide}{Examples of Filters from RFC 2254}
Return all entries in the scope of the search with attribute
\texttt{cn} having the value ``Babs Jensen'':
\begin{verbatim}
(cn=Babs Jensen)
\end{verbatim}
Return all entries in the scope of the search which do \texttt{not}
have the attribute \texttt{cn} with the value ``Tim Howes'':
\begin{verbatim}
(!(cn=Tim Howes))
\end{verbatim}
Return all entries in the scope of the search which have the attibute 
\begin{verbatim}
(&(objectClass=Person)(|(sn=Jensen)(cn=Babs J*)))
\end{verbatim}
Return all entries having an attribute \texttt{o} (i.e., organisation)
which contains the strings \texttt{univ}, \texttt{of}, \texttt{mich}
with zero or more of any characters between, and with any number of
any characters at the end.
\begin{verbatim}
(o=univ*of*mich*)
\end{verbatim}
\end{slide}

\begin{slide}{More Filter Examples}
  \begin{itemize}
  \item Note that a filter such as \texttt{(age>21)} is not allowed.
  \item Use \texttt{(!(age<=21))} instead.
  \item Similarly, instead of \texttt{(age<21)}, use
    \texttt{(!(age>=21))}.
  \item search for all students in group X, year 3, \CSA course, who
    enrolled this year:
\begin{alltt}
(&(year=3)(course=41300)(classcode=W)
(registrationDate=*-03))
\end{alltt}
   Note that there is a substring match on \texttt{registrationDate}
   here.  A substring match is like a wildcard in filename matching.
  \end{itemize}
\end{slide}

\begin{slide}{Escaping Characters in a Filter}
  \begin{tabularx}{0.9\slideWidth}{Y>{\ttfamily}l}
    \toprule%
    \textbf{Character} & \textbf{Escape Sequence}\\
    \midrule%
    \texttt{*} (asterisk) & \bs2A\\
    \texttt{(} (left parenthesis) & \bs28 \\
    \texttt{)} (right parenthesis) & \bs29 \\
    \texttt{\bs} (backslash) & \bs5C \\
    \texttt{NUL} (the null byte) & \bs00 \\
    \bottomrule
  \end{tabularx}
\end{slide}

\begin{slide}{Using the command line tool ldapsearch}
  \label{sld:using-ldapsearch-with-filter}
  \begin{itemize}
  \item 
\begin{alltt}
$ \textbf{ldapsearch -x -h ldap.vtc.edu.hk \bs
-b "dc=vtc.edu.hk" \bs
"(&(department=ICT)(site=TY)
(|(acType=STF)
(&(year=3)(course=41300)(classcode=W))))" cn}
\end{alltt}%$
\item The result is a list of all the DNs that match the filter, with
  the students' and staff names.
\item Can filter out the DNs and blank lines by piping the command
  though \texttt{grep '\wHt{}cn:' | sort}
\end{itemize}
\end{slide}

\begin{slide}{Output of this \texttt{ldapsearch} without staff}
  \label{sld:using-ldapsearch-output}
  \ptsize{8}
\begin{verbatim}
cn: CHAN Kwok Kam
cn: CHEUK Suk Lai
cn: CHUNG Ming Kit
cn: LAI Man Chiu
cn: LAM Lai Hang
cn: LAU Siu Ying
cn: LAW Yuk Woon
cn: LI Kim Wah
cn: LI Siu Kai
cn: LI Yuet Cheung
cn: MA Hei Man
cn: MO Hoi Yu
cn: POON Chun Chung
cn: TAM Kin Fai
cn: TSO Yee Yee
cn: WONG Chi Man
cn: WONG Hoi Shan
cn: WONG Siu Fai
cn: WOO Kin Fan
\end{verbatim}
\end{slide}

\begin{slide}{Get All the Results}
\ptsize{8}\begin{alltt}\small
$ \textbf{ldapsearch -x -h ldap.vtc.edu.hk -b 'dc=vtc.edu.hk' \bs
"(&(department=ICT)(site=TY)(|(actype=STF)(&(year=3)
(classcode=W)(course=41300))))" cn \bs
| grep '^cn: ' | sed '{s/^cn: //;s/^\bs(.\bs\{15\bs\}\bs).*/\bs1/}' | sort | column}
Andy LAI        C M Ho          LEE HUNG KIN    SIU CHONG PUI
CHAN CHIN PANG  Curtis H.K. Tsa LEE KOON HUNG K SIU WAI CHEUNG
CHAN Kwok Kam   Esther YUEN     LEUNG KAM SHEK  Stella Chu
CHAN KWOK KEUNG Eva Chung       LI Kim Wah      TAM CHI HO
CHAN SHIU CHUAN FONG CHI KIT    LI Siu Kai      TAM Kin Fai
CHAN TAI HING   Henry Leung     LI Yuet Cheung  TSANG KWOK TUNG
CHAN TAI MING R HO CHUN WAH     MA Hei Man      TSO Yee Yee
Charles Wu      HO KIM MAN ALBE MA SUI WAH      WONG Chi Man
CHEUK Suk Lai   Josephine Wan   MICHAEL LEUNG   WONG Hoi Shan
CHEUNG KAM HOI  Karl Leung      MO Hoi Yu       WONG Siu Fai
CHEUNG SAI MING Ken LI          MONTAGUE NIGEL  WONG WAI YIP FR
CHIK FUNG YING  Kit K. KO       NG HOI KOW      Wong Y.L. Lawre
CHIU SUET FAN J LAI HING BIU    NG SZE CHIU EDD WOO HUNG CHEUNG
Chou Siu Chuen  LAI Man Chiu    Nick Urbanik    WOO Kin Fan
CHUNG Ming Kit  LAM Lai Hang    PATRICK K.S. TO YIM KWOK HO
CHU SHING TSU J LAU KWOK ON     POON Chun Chung Y.K. Leung
Clarence Lau    LAU Siu Ying    Rick Liu
Clarence Lo     LAW Yuk Woon    SCOTT ALBERT HE
\end{alltt} 
\end{slide}

\begin{slide}{\texttt{ldapsearch}}
  \label{sld:using-ldapsearch-3-bind}
  \begin{itemize}
  \item Needs the \texttt{-x} option to work here
  \item Check ssl works with the \texttt{-ZZ} option
  \item Can ``bind'' as a user to get all the info you are allowed to
    see after binding:
\begin{alltt}\footnotesize
$ \textbf{ldapsearch -x -W -D \bs
"uid=nicku,ou=People,dc=tyict,dc=vtc,dc=edu,dc=hk" \bs
'(uid=nicku)'}
\end{alltt}%$
  \item Can then see own passwords
  \end{itemize}
\end{slide}

\begin{slide}{\LDAP URLs: RFC 2255}
  \begin{itemize}
  \item Have the form:
  \item
  \texttt{ldap://\meta{host}:\meta{port}/\meta{base}?\meta{attr}?\meta{scope}?\meta{filter}}
  {\footnotesize
\begin{verbatim}
ldapurl    = ldap://" [hostport] ["/"
                   [dn ["?" [attributes] ["?" [scope]
                   ["?" [filter] ["?" extensions]]]]]]
\end{verbatim}%
}

\item The \meta{base} or \texttt{dn} is the distinguished name of the
  starting entry for your search.
\item \meta{scope} is one of \texttt{base}, \texttt{one} or \texttt{sub}
\item Examples:
{\tiny
\begin{verbatim}
ldap://ictlab/ou=People,dc=tyict,dc=vtc,dc=edu,dc=hk?uid?one?(uid=nicku)
\end{verbatim}%
}
  %% \item Can enter this into Netscape 4.7.x to see \LDAP entry for me:
%% \item ldap://ictlab/ou=People,dc=tyict,dc=vtc,dc=edu,dc=hk??one?(uid=nicku)
\end{itemize}
\end{slide}

\begin{slide}{\texttt{mod\_auth\_ldap} with Apache}
\ptsize{11}
\begin{itemize}
\item \texttt{mod\_auth\_ldap} is part of the \texttt{httpd} \RPM
  package on Fedora Core~1.
\item Here we allow staff or students from group W, year 3 \CSA to
  access the web pages under \url{http://hostname/group-w/} if the user
  provides a correct password:
{\scriptsize
\begin{verbatim}
<Location "/group-w">
     AuthType Basic
     AuthName ``\LDAP authentication to class W only"
     AuthLDAPURL ldap://ldap.tyict.vtc.edu.hk/
ou=People,dc=tyict,dc=vtc,
dc=edu,dc=hk?uid?one?(|(acType=STF)(\&(course=41300)
(classCode=W)(year=3)))
     require valid-user
</Location>
\end{verbatim}%
}
\item \tiny See {\tiny
    \url{http://httpd.apache.org/docs-2.0/mod/mod_auth_ldap.html}},
  and also
  {\tiny\url{http://httpd.apache.org/docs-2.0/mod/mod_ldap.html}}
  for manual.
\end{itemize}
\end{slide}

\tsection{ICT Schema Design}

\begin{slide}{Authorisation of Students and Staff}
\begin{itemize}
\item We need a new schema to support the required attributes
\item We create three new objectClasses and associated attributes:
\item The first is common to students and staff:
{\scriptsize
\begin{verbatim}
objectclass ( 1.3.6.1.4.1.11400.2.2.1 NAME 'institute'
  SUP top AUXILIARY
  DESC 'Any person in the institute, staff or student'
  MAY ( acOwner $ acType $ answer1 $ answer2 $
        answer3 $ batchUpdateFlag $ department $
        site $ instituteEmail ) )
\end{verbatim}%
}
\end{itemize}
\end{slide}

\begin{slide}{Other objectTypes for IVE}
\begin{itemize}
\item Then on top of this, we have attributes for students:
{\footnotesize
\begin{verbatim}
objectclass ( 1.3.6.1.4.1.11400.2.2.2 NAME 'student'
        SUP top AUXILIARY
        DESC 'A student in the institute'
  MAY ( academicYear $ award $ classCode $ course $
        courseDuration $ FinalYear $
        registrationDate $year $
        fullPartTime ) )
\end{verbatim}%
}
\item \ldots and staff:
{\footnotesize
\begin{verbatim}
objectclass ( 1.3.6.1.4.1.11400.2.2.3 NAME 'staff'
        SUP top AUXILIARY
        DESC 'A staff member of the insitute.'
  MAY ( titleDes $ employerID ) )
\end{verbatim}%
}
\end{itemize}
\end{slide}

\begin{slide}{The whole schema for IVE}
  \begin{itemize}
  \item The whole schema can be seen here:
    \footnotesize
    \url{http://nicku.org/oids/institute.schema}
  \end{itemize}
\end{slide}

\begin{slide}{Case Study: ICT laboratories}
  \begin{itemize}
  \item Old system:
  \item An ancient \acro{DEC} Alpha running \NIS
  \item Hardware insufficient for demand
  \item \emphcolour{Very} expensive maintenance, stopped paying
  \item Technician reported a hardware failure close to first day of term
  \item New system:
  \item We were planning to introduce \LDAP authentication gradually
  \item Failure required planning move faster
  \item Needed to maintain old legacy accounts, plus introduce new
    accounts
\end{itemize}
\end{slide}

\begin{slide}{ICT case study}
  \begin{itemize}
  \item We chose Open\LDAP on Linux
  \item Running on an Acer Altos dual \CPU P-III
  \item Migrated from the \NIS using the migration scripts provided
    with Open\LDAP
  \item Migrated from the \VTC \LDAP accounts using a Perl program,
    written (quickly!) for the purpose,
  \item Uses the \texttt{Net::LDAP} Perl modules
  \end{itemize}
\end{slide}

\begin{slide}{ICT case study --- 2}
  \begin{itemize}
  \item After migrating the legacy accounts, and creating new accounts
    for staff, full and part time students, had more than 5000
    accounts
  \item The \LDAP server was using a high \CPU load
  \item Was able to solve this using caching:
  \item Use \texttt{nscd} (name service caching daemon) on client
  \item Use memory in server to increase local cache size drastically.
  \item \CPU load reduced to a very acceptable level.
  \end{itemize}
\end{slide}

\tsection{Flat, Hierarchical Structures}

\begin{slide}{Directory Structure --- 1}
  \begin{itemize}
  \item The ICT \LDAP server namespace design:
  \end{itemize}
  \vspace*{4ex}
  \begin{center}
    \includegraphics[width=\slideWidth]{ldap-schema-ict}
  \end{center}
\end{slide}

\begin{slide}{Directory Structure --- 2}
\begin{itemize}
\item We chose a fairly flat directory structure
\item Recommended by reference, pages 239, 249.
\item Reason: flexibility:
\item allows for change without major reorganisation of data.
\end{itemize}
\end{slide}

\begin{slide}{Hierarchical Directory Structure}
  \begin{itemize}
  \item This directory structure is hierarchical:
  \end{itemize}
  \vspace*{2ex}
  \begin{center}
    \includegraphics[width=\slideWidth]{ldap-schema-hierarchical}
  \end{center}
\end{slide}

\begin{slide}{New VTC \LDAP Namespace}
  \begin{itemize}
  \item This new \VTC \LDAP namespace was introduced in April 2003:
  \end{itemize}
  \vspace*{2ex}
  \begin{center}
    \includegraphics[width=\slideWidth]{ldap-schema-vtc-2003}
  \end{center}
\end{slide}

\begin{slide}{Hierarchical Directory Structure}
\begin{itemize}
\item This is an alternative data arrangement
\item Divide into different campuses
\item Advantage: can easily delegate management to local campus
\item But: suppose ENG changes to EE?
\item Suppose staff move from one department to another?
\item Suppose equipment is transferred?
\item Not only need change the attributes in the entry, but also move the entry.
\item Overall, a flatter structure is easier to manage.
\end{itemize}
\end{slide}

\begin{slide}{Directory Design Guidelines}
\begin{itemize}
\item Design as flat as possible given constraints:
\item Replication
\item Access Control
\item Limitations of directory software
\item Requirements of applications that use the directory
\end{itemize}
\end{slide}

\begin{slide}{Designing a Schema}
\begin{itemize}
\item After selecting the schema attributes needed for your application, you may find that not all are available with the server
\item Search web for more schemas
\item If none provide all you need,
\item Select a suitable structural base class
\item Create an auxiliary class to be used with the base class
\item Define the objectClass and its attributes
\end{itemize}
\end{slide}

\begin{slide}{Designing a Schema: Example}
  \begin{itemize}
  \item For our \ICT \LDAP server, we use enough attributes to be able
    to log in
  \item But we also want to select users on the basis of course, year,
    class
  \item Want to add these attributes to the existing objectClasses
  \item Create three object classes:
  \item Institute
  \item Student
  \item Staff
  \end{itemize}
\end{slide}

\tsection{References}

\begin{slide}{References}
  \ptsize{10}\footnotesize
  \begin{itemize}
  \item \emph{LDAP System Administration}, Gerald Carter, ISBN
    1-565-92491-6, O'Reilly, March 2003
  \item \emph{Understanding and Deploying LDAP Directory Services}
    (2nd Edition), Tim Howes, Timothy A. Howes, Mark C. Smith, Gordon
    S.  Good, ISBN: 0672323168, Publisher: Addison Wesley
    Professional, May 2, 2003
  \item \emph{Understanding and Deploying LDAP Directory Services},
    Timothy Howes, Mark Smith and Gordon Good, Macmillan, 1999. Our
    library: TK 5105.595.H69 1999
  \item \emph{LDAP Programming, Management and Integration}, Clayton
    Donley, ISBN: 1-930110-40-5, Manning Publications, 2003
  \item \emph{LDAP Directories Explained: An Introduction and
      Analysis}, Brian Arkills, ISBN 0-201-78792-X, Addison-Wesley,
    2003.
  \item \emph{Understanding LDAP Redbook} (registration required):
    \url{http://www.redbooks.ibm.com/abstracts/sg244986.html}
  \item \emph{LDAP Implementation Cookbook Redbook} (registration
    required):
    \url{http://www.redbooks.ibm.com/abstracts/sg245110.html}
  \item \emph{Implementing LDAP}, Mark Wilcox, Wrox Press, 2000
  \end{itemize}
\end{slide}
\end{document}
