.TH SLAPD_META 5 "28 April 2002" "OpenLDAP LDVERSION" .\" Copyright 1998-2002 The OpenLDAP Foundation, All Rights Reserved. .\" Copying restrictions apply. See the COPYRIGHT file. .\" Copyright 2001, Pierangelo Masarati, All rights reserved. .\" $OpenLDAP$ .\" .\" Portions of this document should probably be moved to slapd-ldap(5) .\" and maybe manual pages for librewrite. .\" .SH NAME slapd_meta \- metadirectory backend .SH SYNOPSIS ETCDIR/slapd.conf .SH DESCRIPTION The .B meta backend to .BR slapd (8) performs basic LDAP proxying with respect to a set of remote LDAP servers, called "targets". The information contained in these servers can be presented as belonging to a single Directory Information Tree (DIT). .LP A basic knowledge of the functionality of the .BR slapd\-ldap (5) backend is recommended. This backend has been designed as an enhancement of the ldap backend. The two backends share many features (actually they also share portions of code). While the .B ldap backend is intended to proxy operations directed to a single server, the .B meta backend is mainly intended for proxying of multiple servers and possibly naming context masquerading. These features, although useful in many scenarios, may result in excessive overhead for some applications, so its use should be carefully considered. In the examples section, some typical scenarios will be discussed. .SH EXAMPLES There are examples in various places in this document, as well as in the slapd/back-meta/data/ directory in the OpenLDAP source tree. .SH CONFIGURATION The .BR slapd.conf (5) options in this category apply to the META backend database. That is, they must follow a "database meta" line and come before any subsequent "backend" or "database" lines. .LP Note: as with the .B ldap backend, operational attributes related to entry creation/modification should not be used, as they would be passed to the target servers, generating an error. Moreover, it makes little sense to use such attributes in proxying, as the proxy server doesn't actually store data, so it should have no knowledge of such attributes. While code to strip the modification attributes has been put in place (and #ifdef'd), it implies unmotivated overhead. So it is strongly recommended to set .LP .nf lastmod off .fi .LP for every .B ldap and .B meta backend. .SH "SPECIAL CONFIGURATION DIRECTIVES" Target configuration starts with the "uri" directive. All the configuration directives that are not specific to targets should be defined first for clarity, including those that are common to all backends. They are: .TP .B default-target none This directive forces the backend to reject all those operations that must resolve to a single target in case none or multiple targets are selected. They include: add, delete, modify, modrdn; compare is not included, as well as bind since, as they don't alter entries, in case of multiple matches an attempt is made to perform the operation on any candidate target, with the constraint that at most one must succeed. This directive can also be used when processing targets to mark a specific target as default. .TP .B dncache-ttl {forever|disabled|} This directive sets the time-to-live of the dn cache. This caches the target that holds a given dn to speed up target selection in case multiple targets would result from an uncached search; forever means cache never expires; disabled means no dn caching; otherwise a valid ( > 0 ) ttl in seconds is required. .SH "TARGET SPECIFICATION" Target specification starts with a "uri" directive: .TP .B uri ://[[:]]/ The "server" directive that was allowed in the LDAP backend (although deprecated) has been discarded in the Meta backend. The part can be anything ldap_initialize(3) accepts ({ldap|ldaps|ldapi} and variants); and may be omitted, defaulting to whatever is set in /etc/ldap.conf The part is mandatory. It must end with one of the naming contexts defined for the backend, e.g.: .LP .nf suffix "dc=foo,dc=com" uri "ldap://x.foo.com/dc=x,dc=foo,dc=com" .fi .LP The part doesn't need to be unique across the targets; it may also match one of the values of the "suffix" directive. .TP .B default-target [] The "default-target" directive can also be used during target specification. With no arguments it marks the current target as the default. The optional number marks target as the default one, starting from 1. Target must be defined. .TP .B binddn This directive, as in the LDAP backend, allows to define the dn that is used to query the target server for acl checking; it should have read access on the target server to attributes used on the proxy for acl checking. There is no risk of giving away such values; they are only used to check permissions. .TP .B bindpw This directive sets the password for acl checking in conjunction with the above mentioned "binddn" directive. .TP .B pseudorootdn This directive, if present, sets the dn that will be substituted to the bind dn if a bind with the backend's "rootdn" succeeds. The true "rootdn" of the target server ought not be used; an arbitrary administrative dn should used instead. .TP .B pseudorootpw This directive sets the credential that will be used in case a bind with the backend's "rootdn" succeeds, and the bind is propagated to the target using the "pseudorootdn" dn. .LP Note: cleartext credentials must be supplied here; as a consequence, using the pseudorootdn/pseudorootpw directives is inherently unsafe. .TP .B rewrite* ... The rewrite options are described in the "REWRITING" section. .TP .B suffixmassage All the directives starting with "rewrite" refer to the rewrite engine that has been added to slapd. The "suffixmassage" directive was introduced in the LDAP backend to allow suffix massaging while proxying. It has been obsoleted by the rewriting tools. However, both for backward compatibility and for ease of configuration when simple suffix massage is required, it has been preserved. It wraps the basic rewriting instructions that perform suffix massaging. .LP Note: this also fixes a flaw in suffix massaging, which operated on (case insensitive) DNs instead of normalized DNs, so "dc=foo, dc=com" would not match "dc=foo,dc=com". .LP See the "REWRITING" section. .TP .B map {objectClass|attribute} {|*} [|*] This maps object classes and attributes as in the LDAP backend. See .BR slapd-ldap (5). .SH "SCENARIOS" A powerful (and in some sense dangerous) rewrite engine has been added to both the LDAP and Meta backends. While the former can gain limited beneficial effects from rewriting stuff, the latter can become an amazingly powerful tool. .LP Consider a couple of scenarios first. .LP 1) Two directory servers share two levels of naming context; say "dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then, an unambiguous Meta database can be configured as: .LP .nf database meta suffix "dc=foo,dc=com" uri "ldap://a.foo.com/dc=a,dc=foo,dc=com" uri "ldap://b.foo.com/dc=b,dc=foo,dc=com" .fi .LP Operations directed to a specific target can be easily resolved because there are no ambiguities. The only operation that may resolve to multiple targets is a search with base "dc=foo,dc=com" and scope at least "one", which results in spawning two searches to the targets. .LP 2a) Two directory servers don't share any portion of naming context, but they'd present as a single DIT [Caveat: uniqueness of (massaged) entries among the two servers is assumed; integrity checks risk to incur in excessive overhead and have not been implemented]. Say we have "dc=bar,dc=org" and "o=Foo,c=US", and we'd like them to appear as branches of "dc=foo,dc=com", say "dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then we need to configure our Meta backend as: .LP .nf database meta suffix "dc=foo,dc=com" uri "ldap://a.bar.com/dc=a,dc=foo,dc=com" suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org" uri "ldap://b.foo.com/dc=b,dc=foo,dc=com" suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US" .fi .LP Again, operations can be resolved without ambiguity, although some rewriting is required. Notice that the virtual naming context of each target is a branch of the database's naming context; it is rewritten back and forth when operations are performed towards the target servers. What "back and forth" means will be clarified later. .LP When a search with base "dc=foo,dc=com" is attempted, if the scope is "base" it fails with "no such object"; in fact, the common root of the two targets (prior to massaging) does not exist. If the scope is "one", both targets are contacted with the base replaced by each target's base; the scope is derated to "base". In general, a scope "one" search is honored, and the scope is derated, only when the incoming base is at most one level lower of a target's naming context (prior to massaging). .LP Finally, if the scope is "sub" the incoming base is replaced by each target's unmassaged naming context, and the scope is not altered. .LP 2b) Consider the above reported scenario with the two servers sharing the same naming context: .LP .nf database meta suffix "dc=foo,dc=com" uri "ldap://a.bar.com/dc=foo,dc=com" suffixmassage "dc=foo,dc=com" "dc=bar,dc=org" uri "ldap://b.foo.com/dc=foo,dc=com" suffixmassage "dc=foo,dc=com" "o=Foo,c=US" .fi .LP All the previous considerations hold, except that now there is no way to unambiguously resolve a DN. In this case, all the operations that require an unambiguous target selection will fail unless the dn is already cached or a default target has been set. .SH ACLs Note on ACLs: at present you may add whatever ACL rule you desire to to the Meta (and LDAP) backends. However, the meaning of an ACL on a proxy may require some considerations. Two philosophies may be considered: .LP a) the remote server dictates the permissions; the proxy simply passes back what it gets from the remote server. .LP b) the remote server unveils "everything"; the proxy is responsible for protecting data from unauthorized access. .LP Of course the latter sounds unreasonable, but it is not. It is possible to imagine scenarios in which a remote host discloses data that can be considered "public" inside an intranet, and a proxy that connects it to the internet may impose additional constraints. To this purpose, the proxy should be able to comply with all the ACL matching criteria that the server supports. This has been achieved with regard to all the criteria supported by slapd except a special subtle case (please drop me a note if you can find other exceptions: ). The rule .LP .nf access to dn="" attr= by dnattr= read by * none .fi .LP cannot be matched iff the attribute that is being requested, , is NOT , and the attribute that determines membership, , has not been requested (e.g. in a search) .LP In fact this ACL is resolved by slapd using the portion of entry it retrieved from the remote server without requiring any further intervention of the backend, so, if the attribute has not been fetched, the match cannot be assessed because the attribute is not present, not because no value matches the requirement! .LP Note on ACLs and attribute mapping: ACLs are applied to the mapped attributes; for instance, if the attribute locally known as "foo" is mapped to "bar" on a remote server, then local ACLs apply to attribute "foo" and are totally unaware of its remote name. The remote server will check permissions for "bar", and the local server will possibly enforce additional restrictions to "foo". .\" .\" If this section is moved, also update the reference in .\" libraries/librewrite/RATIONALE. .\" .SH REWRITING A string is rewritten according to a set of rules, called a `rewrite context'. The rules are based on Regular Expressions (POSIX regex) with substring matching; extensions are planned to allow basic variable substitution and map resolution of substrings. The behavior of pattern matching/substitution can be altered by a set of flags. .LP The underlying concept is to build a lightweight rewrite module for the slapd server (initially dedicated to the LDAP backend). .SH Passes An incoming string is matched agains a set of rules. Rules are made of a match pattern, a substitution pattern and a set of actions. In case of match a string rewriting is performed according to the substitution pattern that allows to refer to substrings matched in the incoming string. The actions, if any, are finally performed. The substitution pattern allows map resolution of substrings. A map is a generic object that maps a substitution pattern to a value. .SH "Pattern Matching Flags" .TP .B `C' honors case in matching (default is case insensitive) .TP .B `R' use POSIX Basic Regular Expressions (default is Extended) .SH "Action Flags" .TP .B `:' apply the rule once only (default is recursive) .TP .B `@' stop applying rules in case of match. .TP .B `#' stop current operation if the rule matches, and issue an `unwilling to perform' error. .TP .B `G{n}' jump n rules back and forth (watch for loops!). Note that `G{1}' is implicit in every rule. .TP .B `I' ignores errors in rule; this means, in case of error, e.g. issued by a map, the error is treated as a missed match. The `unwilling to perform' is not overridden. .LP The ordering of the flags is significant. For instance: `IG{2}' means ignore errors and jump two lines ahead both in case of match and in case of error, while `G{2}I' means ignore errors, but jump thwo lines ahead only in case of match. .LP More flags (mainly Action Flags) will be added as needed. .SH "Pattern matching:" See .BR regex (7). .SH "String Substitution:" The string substitution happens according to a substitution pattern. .TP .B - substring substitution is allowed with the syntax `\\d' where `d' is a digit ranging 0-9 (0 is the full match). I see that 0-9 digit expansion is a widely accepted practise; however there is no technical reason to use such a strict limit. A syntax of the form `\\{ddd}' should be fine if there is any need to use a higher number of possible submatches. .TP .B - variable substitution will be allowed (at least when I figure out which kind of variable could be proficiently substituted) .TP .B - map lookup will be allowed (map lookup of substring matches in gdbm, ldap(!), math(?) and so on maps `a la sendmail'. .TP .B - subroutine invocation will make it possible to rewrite a submatch in terms of the output of another rewriteContext. .Sh "Old syntax:" .TP .B `\\' {0-9} [ `{' [ `(' `)' ] `}' ] where is the name of a built-in map, and are optional arguments to the map, if the map requires them. The following experimental maps have been implemented: .TP .B \\n{xpasswd} maps the n-th substring match as uid to the gecos field in /etc/passwd; .TP .B \\n{xfile(/absolute/path)} maps the n-th substring match to a `key value' style plain text file. .TP .B \\n{xldap(ldap://url/with?%0?in?filter) maps the n-th substring match to an attribute retrieved by means of an LDAP url with substitution of %0 in the filter (NOT IMPL.) .SH "New scheme:" everything starting with `\\' requires substitution; .LP the only obvious exception is `\\\\', which is left as is; .LP the basic substitution is `\\d', where `d' is a digit; 0 means the whole string, while 1-9 is a submatch; .LP in the outdated schema, the digit may be optionally followed by a `{', which means pipe the submatch into the map described by the string up to the following `}'; .LP the output of the map is used instead of the submatch; .LP in the new schema, a `\\' followed by a `{' invokes an advanced substitution scheme. The pattern is: .LP .nf `\\' `{' [{ }] `(' `)' `}' .fi .LP where must be a legal name for the map, i.e. .LP .nf ::= [a-z][a-z0-9]* (case insensitive) ::= `>' `|' `&' `&&' `*' `**' `$' .fi .LP and must be a legal substitution schema, with no limits on the nesting level. .LP The operators are: .TP .B > sub context invocation; must be a legal, already defined rewrite context name .TP .B | external command invocation; must refer to a legal, already defined command name (NOT IMPL.) .TP .B & variable assignment; defines a variable in the running operation structure which can be dereferenced later (NOT IMPL.) .TP .B * variable dereferencing; must refer to a variable that is defined and assigned for the running operation (NOT IMPL.) .TP .B $ parameter dereferencing; must refer to an existing parameter; the idea is to make some run-time parameters set by the system available to the rewrite engine, as the client host name, the bind dn if any, constant parameters initialized at config time, and so on (NOT IMPL.) .LP Note: as the slapd parsing routines escape backslashes ('\\'), a double backslash is required inside substitution patterns. To overcome the resulting heavy notation, the substitution escaping has been delegated to the `%' symbol, which should be used instead of `\\' in string substitution patterns. The symbol can be altered at will by redefining the related macro in "rewrite-int.h". In the current snapshot, all the `\\' on the left side of each rule (the regex pattern) must be converted in `\\\\'; all the `\\' on the right side of the rule (the substitution pattern) must be turned into `%'. In the following examples, the original (more readable) syntax is used. .SH "Rewrite context:" A rewrite context is a set of rules which are applied in sequence. The basic idea is to have an application initialize a rewrite engine (think of Apache's mod_rewrite ...) with a set of rewrite contexts; when string rewriting is required, one invokes the appropriate rewrite context with the input string and obtains the newly rewritten one if no errors occur. .LP An interesting application, in the LDAP backend or in slapd itself, could associate each basic server operation to a rewrite context (most of them possibly aliasing the default one). Then, DN rewriting could take place at any invocation of a backend operation. .LP client -> server: .LP .nf default if defined and no specific context is available bindDn bind searchBase search searchFilter search compareDn compare addDn add modifyDn modify modrDn modrdn newSuperiorDn modrdn deleteDn delete .fi .LP server -> client: .LP .nf searchResult search (only if defined; no default) .fi .LP .SH "Basic configuration syntax" .TP .B rewriteEngine { on | off } If `on', the requested rewriting is performed; if `off', no rewriting takes place (an easy way to stop rewriting without altering too much the configuration file). .TP .B rewriteContext [ alias ] is the name that identifies the context, i.e. the name used by the application to refer to the set of rules it contains. It is used also to reference sub contexts in string rewriting. A context may aliase another one. In this case the alias context contains no rule, and any reference to it will result in accessing the aliased one. .TP .B rewriteRule [ ] Determines how a tring can be rewritten if a pattern is matched. Examples are reported below. .SH "Additional configuration syntax:" .TP .B rewriteMap [ ] Allows to define a map that transforms substring rewriting into something else. The map is referenced inside the substitution pattern of a rule. .TP .B rewriteParam Sets a value with global scope, that can be dereferenced by the command `\\{$paramName}'. .TP .B rewriteMaxPasses Sets the maximum number of total rewriting passes taht can be performed in a signle rewriting operation (to avoid loops). .SH "Configuration examples:" .nf # set to `off' to disable rewriting rewriteEngine on # Everything defined here goes into the `default' context. # This rule changes the naming context of anything sent # to `dc=home,dc=net' to `dc=OpenLDAP, dc=org' rewriteRule "(.*)dc=home,[ ]?dc=net" "\\1dc=OpenLDAP, dc=org" ":" # Start a new context (ends input of the previous one). # This rule adds blancs between dn parts if not present. rewriteContext addBlancs rewriteRule "(.*),([^ ].*)" "\\1, \\2" # This one eats blancs rewriteContext eatBlancs rewriteRule "(.*),[ ](.*)" "\\1,\\2" # Here control goes back to the default rewrite # context; rules are appended to the existing ones. # anything that gets here is piped into rule `addBlancs' rewriteContext default rewriteRule ".*" "\\{>addBlancs(\\0)}" ":" # Anything with `uid=username' is looked up in # /etc/passwd for gecos (I know it's nearly useless, # but it is there just to test something fancy!). Note # the `I' flag that leaves `uid=username' in place if # `username' does not have a valid account, and the # `:' that forces the rule to be processed exactly once. rewriteContext uid2Gecos rewriteRule "(.*)uid=([a-z0-9]+),(.+)" "\\1cn=\\2{xpasswd},\\3" "I:" # Finally, in a bind, if one uses a `uid=username' dn, # it is rewritten in `cn=name surname' if possible. rewriteContext bindDn rewriteRule ".*" "\\{>addBlancs(\\{>uid2Gecos(\\0)})}" ":" # Rewrite the search base according to `default' rules. rewriteContext searchBase alias default # Search results with OpenLDAP dn are rewritten back with # `dc=home,dc=net' naming context, with spaces eaten. rewriteContext searchResult rewriteRule "(.*[^ ]?)[ ]?dc=OpenLDAP,[ ]?dc=org" "\\{>eatBlancs(\\1)}dc=home,dc=net" ":" # Bind with email instead of full dn: we first need # an ldap map that turns attributes into a dn (the # filter is provided by the substitution string): rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub" # Then we need to detect emails; note that the rule # in case of match stops rewriting; in case of error, # it is ignored. In case we are mapping virtual # to real naming contexts, we also need to rewrite # regular DNs, because the definition of a bindDn # rewrite context overrides the default definition. rewriteContext bindDn rewriteRule "(mail=[^,]+@[^,]+)" "\\{attr2dn(\\1)}" "@I" # This is a rather sophisticate example. It massages a # search filter in case who performs the search has # administrative privileges. First we need to keep # track of the bind dn of the incoming request: rewriteContext bindDn rewriteRule ".+" "\\{**&binddn(\\0)}" ":" # A search filter containing `uid=' is rewritten only # if an appropriate dn is bound. # To do this, in the first rule the bound dn is # dereferenced, while the filter is decomposed in a # prefix, the argument of the `uid=', and in a # suffix. A tag `<>' is appended to the DN. If the DN # refers to an entry in the `ou=admin' subtree, the # filter is rewritten OR-ing the `uid=' with # `cn='; otherwise it is left as is. This could be # useful, for instance, to allow apache's auth_ldap-1.4 # module to authenticate users with both `uid' and # `cn', but only if the request comes from a possible # `dn: cn=Web auth, ou=admin, dc=home, dc=net' user. rewriteContext searchFilter rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)" "\\{**binddn}<>\\{&prefix(\\1)}\\{&arg(\\2)}\\{&suffix(\\3)}" ":I" rewriteRule "[^,]+,[ ]?ou=admin,[ ]?dc=home,[ ]?dc=net" "\\{*prefix}|(uid=\\{*arg})(cn=\\{*arg})\\{*suffix}" "@I" rewriteRule ".*<>" "\\{*prefix}uid=\\{*arg}\\{*suffix}" .fi .SH "LDAP Proxy resolution (a possible evolution of slapd-ldap(5):" In case the rewritten dn is an LDAP URL, the operation is initiated towards the host[:port] indicated in the url, if it does not refer to the local server. E.g.: .LP .nf rewriteRule \'^cn=root,.*\' \'\\0\' \'G{3}\' rewriteRule \'^cn=[a-l].*\' \'ldap://ldap1.my.org/\\0\' \'@\' rewriteRule \'^cn=[m-z].*\' \'ldap://ldap2.my.org/\\0\' \'@\' rewriteRule \'.*\' \'ldap://ldap3.my.org/\\0\' \'@\' .fi .LP (Rule 1 is simply there to illustrate the `G{n}' action; it could have been written: .LP .nf rewriteRule \'^cn=root,.*\' \'ldap://ldap3.my.org/\\0\' \'@\' .fi .LP with the advantage of saving one rewrite pass ...) .SH "SEE ALSO" .BR slapd.conf (5), .BR slapd\-ldap (5), .BR slapd (8), .BR regex (7).