LIBRARY

OpenLDAP LDAP (libldap, −lldap)

DESCRIPTION

These routines provide various interfaces to the LDAP bind operation. After an association with an LDAP server is made using ldap_init(3), an LDAP bind operation should be performed before other operations are attempted over the connection. An LDAP bind is required when using Version 2 of the LDAP protocol; it is optional for Version 3 but is usually needed due to security considerations.

There are three types of bind calls, ones providing simple authentication, ones providing SASL authentication, and general routines capable of doing either simple or SASL authentication.

SASL (Simple Authentication and Security Layer) can negotiate one of many different kinds of authentication. Both synchronous and asynchronous versions of each variant of the bind call are provided. All routines take ld as their first parameter, as returned from ldap_init(3).

SIMPLE AUTHENTICATION

The simplest form of the bind call is ldap_simple_bind_s(). It takes the DN to bind as in who, and the userPassword associated with the entry in passwd. It returns an LDAP error indication (see ldap_error(3)). The ldap_simple_bind() call is asynchronous, taking the same parameters but only initiating the bind operation and returning the message id of the request it sent. The result of the operation can be obtained by a subsequent call to ldap_result(3).

GENERAL AUTHENTICATION

The ldap_bind() and ldap_bind_s() routines can be used when the authentication method to use needs to be selected at runtime. They both take an extra method parameter selecting the authentication method to use. It should be set to LDAP_AUTH_SIMPLE to select simple authentication. ldap_bind() returns the message id of the request it initiates. ldap_bind_s() returns an LDAP error indication.

SASL AUTHENTICATION

For SASL binds the server always ignores any provided DN, so the dn parameter should always be NULL. ldap_sasl_bind_s() sends a single SASL bind request with the given SASL mechanism and credentials in the cred parameter. The format of the credentials depends on the particular SASL mechanism in use. For mechanisms that provide mutual authentication the server's credentials will be returned in the servercredp parameter. The routine returns an LDAP error indication (see ldap_error(3)). The ldap_sasl_bind() call is asynchronous, taking the same parameters but only sending the request and returning the message id of the request it sent. The result of the operation can be obtained by a subsequent call to ldap_result(3). The result must be additionally parsed by ldap_parse_sasl_bind_result() to obtain any server credentials sent from the server.

Many SASL mechanisms require multiple message exchanges to perform a complete authentication. Applications should generally use ldap_sasl_interactive_bind_s() rather than calling the basic ldap_sasl_bind() functions directly. The mechs parameter should contain a space-separated list of candidate mechanisms to use. If this parameter is NULL or empty the library will query the supportedSASLMechanisms attribute from the server's rootDSE for the list of SASL mechanisms the server supports. The flags parameter controls the interaction used to retrieve any necessary SASL authentication parameters and should be one of:

The interact function uses the provided defaults to handle requests from the SASL library for particular authentication parameters. There is no defined format for the defaults information; it is up to the caller to use whatever format is appropriate for the supplied interact function. The sasl_interact parameter comes from the underlying SASL library. When used with Cyrus SASL this is an array of sasl_interact_t structures. The Cyrus SASL library will prompt for a variety of inputs, including:

See the Cyrus SASL documentation for more details.

Applications which need to manage connections asynchronously may use ldap_sasl_interactive_bind() instead of the synchronous version. A valid mechs parameter must be supplied, otherwise the library will be forced to query the server for a list of supported mechanisms, and this query will be performed synchronously. The other parameters are the same as for the synchronous function, with three additional parameters. The actual SASL mechanism that was used, and the message ID for use with ldap_result() will be returned in rmechp and msgidp, respectively. The value in rmechp must not be modified by the caller and must be passed back on each subsequent call. The message obtained from ldap_result() must be passed in the result parameter. This parameter must be NULL when initiating a new Bind. The caller must free the result message after each call using ldap_msgfree(). The ldap_sasl_interactive_bind() function returns an LDAP result code. If the code is LDAP_SASL_BIND_IN_PROGRESS then the Bind is not complete yet, and this function must be called again with the next result from the server.

REBINDING

The ldap_set_rebind_proc function() sets the process to use for binding when an operation returns a referral. This function is used when an application needs to bind to another server in order to follow a referral or search continuation reference.

The function takes ld, the rebind function, and the params, the arbitrary data like state information which the client might need to properly rebind. The LDAP_OPT_REFERRALS option in the ld must be set to ON for the libraries to use the rebind function. Use the ldap_set_option function to set the value.

The rebind function parameters are as follows:

The ld parameter must be used by the application when binding to the referred server if the application wants the libraries to follow the referral.

The url parameter points to the URL referral string received from the LDAP server. The LDAP application can use the ldap_url_parse(3) function to parse the string into its components.

The request parameter specifies the type of request that generated the referral.

The msgid parameter specifies the message ID of the request generating the referral.

The params parameter is the same value as passed originally to the ldap_set_rebind_proc() function.

The LDAP libraries set all the parameters when they call the rebind function. The application should not attempt to free either the ld or the url structures in the rebind function.

The application must supply to the rebind function the required authentication information such as, user name, password, and certificates. The rebind function must use a synchronous bind method.

UNBINDING

The ldap_unbind() call is used to unbind from the directory, terminate the current association, and free the resources contained in the ld structure. Once it is called, the connection to the LDAP server is closed, and the ld structure is invalid. The ldap_unbind_s() call is just another name for ldap_unbind(); both of these calls are synchronous in nature.

The ldap_unbind_ext() and ldap_unbind_ext_s() allows the operations to specify controls.

ERRORS

Asynchronous routines will return −1 in case of error, setting the ld_errno parameter of the ld structure. Synchronous routines return whatever ld_errno is set to. See ldap_error(3) for more information.

NOTES

If an anonymous bind is sufficient for the application, the rebind process need not be provided. The LDAP libraries with the LDAP_OPT_REFERRALS option set to ON (default value) will automatically follow referrals using an anonymous bind.

If the application needs stronger authentication than an anonymous bind, you need to provide a rebind process for that authentication method. The bind method must be synchronous.

SEE ALSO

ldap(3), ldap_error(3), ldap_open(3), ldap_set_option(3), ldap_url_parse(3) RFC 4422 (http://www.rfc-editor.org), Cyrus SASL (http://asg.web.cmu.edu/sasl/)

ACKNOWLEDGEMENTS

OpenLDAP Software is developed and maintained by The OpenLDAP Project <http://www.openldap.org/>. OpenLDAP Software is derived from University of Michigan LDAP 3.3 Release.