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<p>Currently this class is designed only to satisfy the limited functionality necessary for the <a href="http://framework.zend.com/wiki/x/RJw">Zend_Auth_Adapter_Ldap</a> authentication adapter. Operations such as searching, creating, modifying or renaming entries in the directory are currently not supported and will be defined at a later time.</p></ac:rich-text-body></ac:macro>

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Zend Framework: Zend_Ldap Component Proposal

Proposed Component Name Zend_Ldap
Developer Notes http://framework.zend.com/wiki/display/ZFDEV/Zend_Ldap
Proposers Michael B Allen
Darby Felton, Zend liaison
Revision (wiki revision: 15)

Table of Contents

1. Overview

Zend_Ldap is proposed as a class for performing LDAP operations including but not limited to binding, searching and modifying entries in an LDAP directory.

2. References

3. Component Requirements, Constraints, and Acceptance Criteria

  • This component should throw exceptions for configuration errors, environmental issues and invalid usage (e.g. required options missing, ldap extension unavailable, wrong parameter supplied to method, etc).
  • Currently this component will use the standard ldap extension shipped with PHP.
  • This component must support optional SSL / TLS encrypted transport.

4. Dependencies on Other Framework Components

  • Zend_Ldap_Exception - Zend_Ldap_Exception is a companion class to Zend_Ldap used to handle unexpected LDAP extension errors and LDAP specific protocol errors (e.g. failed to connect to LDAP server).
  • Zend_Exception - Zend_Ldap_Exception extends Zend_Exception

5. Theory of Operation

This component currently consists of two classes Zend_Ldap and Zend_Ldap_Exception. The Zend_Ldap class conceptually represents a binding to a single LDAP server. The parameters for binding may be provided explicitly or in the form of an options array.

Using the Zend_Ldap class depends on the type of LDAP server and is best summarized with some simple examples.

If you are using OpenLDAP a simple example looks like the following (note that the bindRequiresDn option is important if you are not using AD):

require_once 'Zend/Ldap.php';

$options = array(
    'host' => 's0.foo.net',
    'username' => 'CN=user1,DC=foo,DC=net',
    'password' => 'pass1',
    'bindRequiresDn' => true,
    'accountDomainName' => 'foo.net',
    'baseDn' => 'OU=Sales,DC=foo,DC=net',
);
$ldap = new Zend_Ldap($options);
$acctname = $ldap->getCanonicalAccountName('abaker', Zend_Ldap::ACCTNAME_FORM_DN);
echo "$acctname\n";

If you are using Microsoft AD a simple example is:

require_once 'Zend/Ldap.php';

$options = array(
    'host' => 'dc1.w.net',
    'useSsl' => true,
    'username' => 'user1@w.net',
    'password' => 'pass1',
    'accountDomainName' => 'w.net',
    'accountDomainNameShort' => 'W', 
    'baseDn' => 'CN=Users,DC=w,DC=net',
);
$ldap = new Zend_Ldap($options);
$acctname = $ldap->getCanonicalAccountName('bcarter', Zend_Ldap::ACCTNAME_FORM_DN);
echo "$acctname\n";

Note that we use the getCanonicalAccountName() method to retrieve the account DN here only because that is what exercises the most of what little code is currently present in this class.

Automatic Username Canonicalization When Binding

If bind() is called with a non-DN username but bindRequiresDN is true and no username in DN form was supplied as an option, the bind will fail. However, if a username in DN form is supplied in the options array, Zend_Ldap will first bind with that username, retrieve the account DN for the username supplied to bind() and then re-bind with that DN.

This behavior is critical to Zend_Auth_Adapter_Ldap which passes the username supplied by the user directly to bind().

The following example illustrates how the non-DN username 'abaker' can be used with bind():

require_once 'Zend/Ldap.php';

$options = array(
        'host' => 's0.foo.net',
        'username' => 'CN=user1,DC=foo,DC=net',
        'password' => 'pass1',
        'bindRequiresDn' => true,
        'accountDomainName' => 'foo.net',
        'baseDn' => 'OU=Sales,DC=foo,DC=net',
);
$ldap = new Zend_Ldap($options);
$ldap->bind('abaker', 'moonbike55');
$acctname = $ldap->getCanonicalAccountName('abaker', Zend_Ldap::ACCTNAME_FORM_DN);
echo "$acctname\n";

The bind() call in this example sees that the username 'abaker' is not in DN form, finds bindRequiresDn is true, uses 'CN=user1,DC=foo,DC=net' and 'pass1' to bind, retrieves the DN for 'abaker', unbinds and then rebinds with the newly discovered 'CN=Alice Baker,OU=Sales,DC=foo,DC=net'.

Zend_Ldap Options

The Zend_Ldap component accepts an array of options either supplied to the constructor or through the setOptions() method. The permitted options are as follows:

Name Description
host The default hostname of LDAP server if not supplied to connect() (also may be used when trying to canonicalize usernames in bind()).
port Default port of LDAP server if not supplied to connect().
useSsl Whether or not the LDAP client should use SSL / TLS encrypted transport. A value of true is strongly favored in production environments to prevent passwords from be transmitted in clear text. The default value is false as servers frequently require that a certificate be installed separately after installation.
username The default credentials username. Some servers require that this be in DN form.
password The default credentials password (used only with username above).
bindRequiresDn If true, this instructs Zend_Ldap to retrieve the DN for the account used to bind if the username is not already in DN form. The default value is false.
baseDn The default base DN used for searching (e.g. for accounts). This option is required for most account related operations and should indicate the DN under which accounts are located.
accountCanonicalForm A small integer indicating the form account names should be canonicalized to. See the Account Name Canonicalization section below.
accountDomainName The FQDN domain for which the target LDAP server is an authority (e.g. example.com).
accountDomainNameShort The 'short' domain for which the target LDAP server is an authority. This is usually used to specify the NetBIOS domain name for Windows networks but may also be used by non-AD servers.
accountFilterFormat The LDAP search filter used to search for accounts. This string is a printf style expression that must contain one '%s' to accomodate the username. The default value is '(&(objectClass=user)(sAMAccountName=%s))' unless bindRequiresDn is set to true in which case the default is '(&(objectClass=posixAccount)(uid=%s))'. Users of custom schemas may need to change this option.

Account Name Canonicalization

The accountDomainName and accountDomainNameShort options are used for two purposes - 1) they facilitate multi-domain authentication and failover capability and 2) they are also used to canonicalize usernames. Specifically, names are canonicalized to the form specified by the accountCanonicalForm option. This option may one of the following values:

Name Value Example
ACCTNAME_FORM_DN 1 CN=Alice Baker,CN=Users,DC=example,DC=com
ACCTNAME_FORM_USERNAME 2 abaker
ACCTNAME_FORM_BACKSLASH 3 EXAMPLE\abaker
ACCTNAME_FORM_PRINCIPAL 4 abaker@example.com

The default canonicalization depends on what account domain name options were supplied. If accountDomainNameShort was supplied the default accountCanonicalForm value is ACCTNAME_FORM_BACKSLASH. Otherwise, if accountDomainName was supplied, the default is ACCTNAME_FORM_PRINCIPAL.

Account name canonicalization ensures that the string used to identify an account is consistent regardless of what was supplied to bind(). For example, if the user supplies an account name of abaker@example.com or just abaker and the accountCanonicalForm is set to 3, the resulting canonicalized name would be EXAMPLE\abaker.

Multi-domain Authentication and Failover

The Zend_Ldap component by itself makes no attempt to authenticate with multiple servers. However, Zend_Ldap is specifically designed to handle this scenario gracefully. The required technique is to simply iterate over an array of arrays of server options and attempt to bind with each server. As described above bind() will automatically canonicalize each name so it does not matter if the user passes abaker@foo.net or W\bcarter or cdavis - the bind() method will only succeed if the credentials were successfully used in the bind.

Consider the following example that illustrates the technique required to implement multi-domain authentication and failover:

If the bind fails for any reason, the next set of server options is tried.

The getCanonicalAccountName call gets the canonical account name that the application would presumably use to associate data with such as preferences. The accountCanonicalForm = 4 in all server options ensures that the canonical form is consistent regardless of which server was ultimately used.

The special LDAP_X_DOMAIN_MISMATCH exception occurs when an account name with a domain component was supplied (e.g. abaker@foo.net or FOO\abaker and not just abaker) but the domain component did not match either domain in the currently selected server options. Meaning, this exception indicates that the server is not an authority for the account. In this case, the bind will not be performed therby eliminating unnecessary communication with the server. Note that the continue instruction has no effect in this example but in practice for error handling and debugging purposes you will probably want to check for LDAP_X_DOMAIN_MISMATCH as well as LDAP_NO_SUCH_OBJECT and LDAP_INVALID_CREDENTIALS.

The above code is very similar to that of Zend_Auth_Adapter_Ldap. In fact, we recommend that you simply use that authentication adapter for multi-domain + failover LDAP based authentication (or copy the code).

6. Milestones / Tasks

  • Milestone 1: [DONE] Create initial prototype.
  • Milestone 2: [DONE] Create documentation necessary to use and test prototype.
  • Milestone 3: Working prototype checked into the incubator.
  • Milestone 4: Create unit tests

7. Class Index

  • Zend_Ldap
  • Zend_Ldap_Exception

8. Use Cases

See examples herein. Currently this class is used exclusively by the Zend_Auth_Adapter_Ldap authentication adapter and as such there no use-cases other than those associated with binding (used as an authentication mechanism) and account name canonicalization.

9. Class Skeletons

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  1. Jan 17, 2008

    <ac:macro ac:name="note"><ac:parameter ac:name="title">Zend Comments</ac:parameter><ac:rich-text-body>
    <p>This proposal is approved for incubator development.</p></ac:rich-text-body></ac:macro>