The LDAP module is database driver, i.e. it implements DB API functions. The goal is map database query defined by table, matching fields and result fields to LDAP search in sub-tree defined by root, object class, attributes and pass it to the OpenLDAP which communicates with the LDAP server.
This procedure is sometimes tricky because the LDAP does not support all database features or supports them in different manner. Here we must express especially filtering and multi-values. The multi-value is de facto array of single values. If the LDAP module get a multi-value field then generates record for every single value, respectively for every combination in case the more fields contain multi-value.
The LDAP supports natively "AND", "OR", "NOT" logical operators and "equal", "non-equal", "less-or-equal" and "greater-or-equal" comparison operators. Therefore "less" and "greater" operators are mapped as "less/greater-or-equal-AND-not-equal". It's important realize it when the attribute which will be used for filtering may contain multi-value. The LDAP server evaluates comparison operator on multi-value so that the result for record is true if the condition is satisfied for any single value. The single values not satisfying condition are not truncated. It implies two cases for positive comparison, e.g. "equal", the result contains values not satisfying the condition, the case may be handled by additional filter in the LDAP module, the negative comparison, e.g. "non-equal", does not return record at all. Because the LDAP module cannot know if the LDAP attribute may logically contain multi-value so there is introduced DB API option client_side_filtering which forces filtering such fields in the LDAP module, i.e. the LDAP server returns larger result set because the filtering condition is not passed there.
The syntax of client_side_filtering value is comma delimited of field names which won't be used for server-side filter if such a field appears in a match condition. Instead records will be filtered out in module. It implies such fields MUST exist in result field list.
The necessary condition of successful filtering of particular attribute at the LDAP server is correct attribute definition. The "equal"/"non-equal" operator requires equality matching rule, the "greater"/"less" operator requires ordering matching rule. If required matching rule is missing the LDAP server silently returns empty result set. In case of double filtering both at the LDAP servar and the LDAP module, e.g. multi-value and equal comparison, check the LDAP server matching rule satisfies your needs or use client_side_filtering feature.
The LDAP server may be identified either
complete specification of host, user, password in URI or
is specification reference to connection section
of config file. Note in the second case there is only
one slash.
Example 1. URI example
...
modparam("auth", "db_url", "ldap://admin:heslo@127.0.0.1");
modparam("auth", "db_url", "ldap:/ldap_server1");
...
Features:
simple, SASL authentication, TLS
server and client side filtering
read-only queries
optional referral chasing by OpenLDAP
optional reference chasing by OpenLDAP
Default value is ldap.cfg.
The filename (relatively to ser config file) of mapping database to LDAP definition. It is the main configuration file for the LDAP module in SER. The configuration file maps database table names used in SER to LDAP directory sub-trees to be searched. In addition to that the configuration file also allows to configure the LDAP search filter and maps database field names to LDAP attribute names and vice versa.
Example 3. Configuration file example
# Supported Attribute Type Names: # * GeneralizedTime # * Integer # * BitString # * Boolean # * String # * Binary # * Float # [connection:ldap_server1] host=127.0.0.1 port=389 username=ser password=heslo # LDAP or LDAP SASL authentication mechanism. # Allowed values: none (default), simple, digest-md5, external authtype=simple # tls encryption tls=off # Specifies the file that contains certificates for all of the Certificate # Authorities the ldap module will recognize. ca_list=/home/kg/work/openssl/demoCA/cacert.pem # Specifies what checks to perform on server certificates in a TLS session # allowed values are never/allow/try/demand # see the TLS_REQCERT tls option part of ldap.conf(8) man page for more details require_certificate=demand # # Table credentials contains SIP digest authentication credentials. # [table:credentials] # In our LDAP directory we store SIP digest credentials under # "Digest Credentials" organization unit so this is where searches for digest # credentials should start. base = "ou=Digest Credentials,dc=iptel,dc=org" # We search the whole subtree. scope = subtree # For digest credentials we are only interested in objects with objectClass # 'digestAuthCredentials', objects of all other types are ignored. filter = "(objectClass=digestAuthCredentials)" # Mapping of field names to LDAP attribute names and vice versa. Names are # delimited using ':', the first name is database field name as used in SER # modules, the second name (after :) is corresponding LDAP attribute name, # optionally preceeded with LDAP attribute syntax name in parentheses. field_map = password : (Binary) digestPassword field_map = realm : digestRealm field_map = auth_username : digestUsername field_map = uid : serUID field_map = flags : (BitString) serFlags # retrieve at most sizelimit entries for a search #sizelimit = 2147483647 # wait at most timelimit seconds for a search to complete #timelimit = 120 # chase references automatically by OpenLDAP. Default is "never" # chase_references = never | searching | finding | always # chase referrals automatically by OpenLDAP. Default is "no" # chase_referrals = yes | no # # Domain table stores information about virtual domains # [table:domain] # Objects mapping domain IDs to domain names and vice versa are stored # in the subtree with the following root: base = "ou=Domains,dc=iptel,dc=org" scope = subtree # We are only interested in serDomain objects when looking up information # about virtual domains. filter = "(objectClass=serDomain)" field_map = did : (String) serDID field_map = domain : (String) serDomain field_map = flags : (BitString) serFlags # # Table domain_attrs contains domain attributes, domain attributes store # extra information about virtual domains. # [table:domain_attrs] base = "ou=Domains, dc=iptel,dc=org" scope = subtree filter = "(objectClass=serDomainAttr)" field_map = did : serDID field_map = name : serAttrName field_map = type : (Integer) serAttrType field_map = value : serAttrValue field_map = flags : (BitString) serFlags