openldap/doc/man/man5/slapo-rwm.5

.TH SLAPO-RWM 5 "RELEASEDATE" "OpenLDAP LDVERSION"
.\" Copyright 1998-2004 The OpenLDAP Foundation, All Rights Reserved.
.\" Copying restrictions apply.  See the COPYRIGHT file.
.\" Copyright 2004, Pierangelo Masarati, All rights reserved. <ando@sys-net.it>
.\" $OpenLDAP$
.\"
.\" Portions of this document should probably be moved to slapd-ldap(5)
.\" and maybe manual pages for librewrite.
.\"
.SH NAME
slapo-rwm \- rewrite/remap overlay
.SH SYNOPSIS
ETCDIR/slapd.conf
.SH DESCRIPTION
The
.B rwm
overlay to
.BR slapd (8)
performs basic DN/data rewrite and objectClass/attributeType mapping.
Its usage is mostly intended to provide virtual views of existing data
either remotely, in conjunction with the proxy backend described in
.BR slapd-ldap (5),
or locally, in conjunction with the relay backend described in
.BR slapd-relay (5).
.SH MAPPING
An important feature of the
.B rwm
overlay is the capability to map objectClasses and attributeTypes
from the local set (or a subset of it) to a foreign set, and vice versa.
This is accomplished by means of the 
.B rwm-map
directive.
.TP
.B rwm-map "{attribute | objectclass} [<local name> | *] {<foreign name> | *}"
Map attributeTypes and objectClasses from the foreign server to
different values on the local slapd.
The reason is that some attributes might not be part of the local
slapd's schema, some attribute names might be different but serve the
same purpose, etc.
If local or foreign name is `*', the name is preserved.
If local name is omitted, the foreign name is removed.
Unmapped names are preseved if both local and foreign name are `*',
and removed if local name is omitted and foreign name is `*'.
.LP
The local 
.I objectClasses 
and 
.I attributeTypes 
must be defined in the local schema; the foreign ones do not have to.
Note, however, that the decision whether to rewrite or not attributeTypes
with 
.IR "distinguishedName syntax" ,
requires the knowledge of the attributeType syntax.
See the REWRITING section for details.
.LP
Note that when mapping DN-valued attributes from local to remote,
first the DN is rewritten, and then the attributeType is mapped;
while mapping from remote to local, first the attributeType is mapped,
and then the DN is rewritten.
As such, it is important that the local attributeType is appropriately
defined as using the distinguishedName syntax.
Also, note that there are DN-related syntaxes, like nameAndOptionalUID,
whose values are currenlty not rewritten.
.SH SUFFIX MASSAGING
A basic feature of the
.B rwm
overlay is the capability to perform suffix massaging between a virtual
and a real naming context by means of the 
.B rwm-suffixmassage
directive.
.TP
.B rwm-suffixmassage "<virtual naming context>" "<real naming context>"
Shortcut to implement naming context rewriting; the trailing part
of the DN is rewritten from the virtual to the real naming context
in the bindDN, searchDN, searchFilterAttrDN, compareDN, compareAttrDN,
addDN, addAttrDN, modifyDN, modifyAttrDN, modrDN, newSuperiorDN,
deleteDN, exopPasswdDN, and from the real to the virtual naming context
in the searchEntryDN, searchAttrDN and matchedDN rewrite contexts.
By default no rewriting occurs for the searchFilter rewrite context.
This directive implies setting the
.B rwm-rewriteEngine
to
.BR ON .
.LP
See the REWRITING section for details.
.SH REWRITING
A string is rewritten according to a set of rules, called a `rewrite
context'.
The rules are based on POSIX (''extended'') regular expressions with
substring matching; basic variable substitution and map resolution 
of substrings is allowed by specific mechanisms detailed in the following.
The behavior of pattern matching/substitution can be altered by a set
of flags.
.LP
.RS
.nf
<rewrite context> ::= <rewrite rule> [...]
<rewrite rule> ::= <pattern> <action> [<flags>]
.fi
.RE
.LP
The underlying concept is to build a lightweight rewrite module
for the slapd server (initially dedicated to the LDAP backend):
.LP
.SH Passes
An incoming string is matched agains a set of 
.IR rewriteRules .
Rules are made of a 
.IR "regex match pattern" , 
a 
.I "substitution pattern"
and a set of actions, described by a set of 
.IR "optional flags" .
In case of match, 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.
Each rule is executed recursively, unless altered by specific action 
flags; see "Action Flags" for details.
A default limit on the recursion level is set, and can be altered
by the
.B rwm-rewriteMaxPasses
directive, as detailed in the "Additional Configuration Syntax" section.
The substitution pattern allows map resolution of substrings.
A map is a generic object that maps a substitution pattern to a value.
The flags are divided in "Pattern Matching Flags" and "Action Flags";
the former alter the regex match pattern behavior, while the latter
alter the actions that are taken after substitution.
.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'')
.TP
.B `M{n}'
allow no more than
.B n
recursive passes for a specific rule; does not alter the max total count
of passes, so it can only enforce a stricter limit for a specific rule.
.SH "Action Flags"
.TP
.B `:'
apply the rule once only (default is recursive)
.TP
.B `@'
stop applying rules in case of match; the current rule is still applied 
recursively; combine with `:' to apply the current rule only once 
and then stop.
.TP
.B `#'
stop current operation if the rule matches, and issue an `unwilling to
perform' error.
.TP
.B `G{n}'
jump
.B 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.
.TP
.B `U{n}'
uses
.B
n
as return code if the rule matches; the flag does not alter the recursive
behavior of the rule, so, to have it performed only once, it must be used 
in combination with `:', e.g.
.B `:U{16}'
returns the value `16' after exactly one execution of the rule, if the
pattern matches.
As a consequence, its behavior is equivalent to `@', with the return
code set to
.BR n ;
or, in other words, `@' is equivalent to `U{0}'.
By convention, the freely available codes are above 16 included;
the others are reserved.
.LP
The ordering of the flags can be 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 two 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)
and/or
.BR re_format (7).
.SH "Substitution Pattern Syntax"
Everything starting with `$' requires substitution;
.LP
the only obvious exception is `$$', which is left as is;
.LP
the basic substitution is `$<d>', where `<d>' is a digit;
0 means the whole string, while 1-9 is a submatch, as discussed in 
.BR regex (7)
and/or
.BR re_format (7).
.LP
a `$' followed by a `{' invokes an advanced substitution.
The pattern is:
.LP
.RS
`$' `{' [ <operator> ] <name> `(' <substitution> `)' `}'
.RE
.LP
where <name> must be a legal name for the map, i.e.
.LP
.RS
.nf
<name> ::= [a-z][a-z0-9]* (case insensitive)
<operator> ::= `>' `|' `&' `&&' `*' `**' `$'
.fi
.RE
.LP
and <substitution> must be a legal substitution
pattern, with no limits on the nesting level.
.LP
The operators are:
.TP
.B >
sub-context invocation; <name> must be a legal, already defined
rewrite context name
.TP
.B |
external command invocation; <name> must refer to a legal, already
defined command name (NOT IMPLEMENTED YET)
.TP
.B &
variable assignment; <name> defines a variable in the running
operation structure which can be dereferenced later; operator
.B &
assigns a variable in the rewrite context scope; operator
.B &&
assigns a variable that scopes the entire session, e.g. its value
can be derefenced later by other rewrite contexts
.TP
.B *
variable dereferencing; <name> must refer to a variable that is
defined and assigned for the running operation; operator
.B *
dereferences a variable scoping the rewrite context; operator
.B **
dereferences a variable scoping the whole session, e.g. the value
is passed across rewrite contexts
.TP
.B $
parameter dereferencing; <name> 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;
no parameter is currently set by either 
.B back\-ldap
or
.BR back\-meta ,
but constant parameters can be defined in the configuration file
by using the
.B rewriteParam
directive.
.LP
Substitution escaping has been delegated to the `$' symbol, 
which is used instead of `\e' in string substitution patterns
because `\e' is already escaped by slapd's low level parsing routines;
as a consequence, regex escaping requires
two `\e' symbols, e.g. `\fB.*\e.foo\e.bar\fP' must
be written as `\fB.*\e\e.foo\e\e.bar\fP'.
.\"
.\" The symbol can be altered at will by redefining the related macro in
.\" "rewrite-int.h".
.\"
.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
Each basic server operation is associated to a rewrite context;
they are divided in two main groups: client \-> server and
server \-> client rewriting.
.LP
client -> server:
.LP
.RS
.nf
(default)            if defined and no specific context 
                     is available
bindDN               bind
searchDN             search
searchFilter         search
searchFilterAttrDN   search
compareDN            compare
compareAttrDN        compare AVA
addDN                add
addAttrDN            add AVA (including "ref")
modifyDN             modify
modifyAttrDN         modify AVA (including "ref")
modrDN               modrdn
newSuperiorDN        modrdn
deleteDN             delete
exopPasswdDN         passwd exop DN
.fi
.RE
.LP
server -> client:
.LP
.RS
.nf
searchEntryDN        search (only if defined; no default;
                     acts on DN of search entries)
searchAttrDN         search AVA (only if defined; defaults
                     to searchEntryDN; acts on DN-syntax
                     attributes of search results)
matchedDN            all ops (only if applicable; defaults
                     to searchEntryDN)
referralDN           all ops (only if applicable; defaults
                     to searchEntryDN)
.fi
.RE
.LP
.SH "Basic Configuration Syntax"
All rewrite/remap directives start with the prefix
.BR rwm- ;
for backwards compatibility with the historical
.BR slapd-ldap (5)
and
.BR slapd-meta (5)
builtin rewrite/remap capabilities, the prefix may be omitted, 
but this practice is strongly discouraged.
.TP
.B rwm-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 rwm-rewriteContext <context name> "[ alias <aliased context name> ]"
<Context name> 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 rwm-rewriteRule "<regex match pattern>" "<substitution pattern>" "[ <flags> ]"
Determines how a string can be rewritten if a pattern is matched.
Examples are reported below.
.SH "Additional Configuration Syntax"
.TP
.B rwm-rewriteMap "<map type>" "<map name>" "[ <map attrs> ]"
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 rwm-rewriteParam <param name> <param value>
Sets a value with global scope, that can be dereferenced by the
command `${$paramName}'.
.TP
.B rwm-rewriteMaxPasses <number of passes> [<number of passes per rule>]
Sets the maximum number of total rewriting passes that can be
performed in a single rewrite operation (to avoid loops).
A safe default is set to 100; note that reaching this limit is still
treated as a success; recursive invocation of rules is simply 
interrupted.
The count applies to the rewriting operation as a whole, not 
to any single rule; an optional per-rule limit can be set.
This limit is overridden by setting specific per-rule limits
with the `M{n}' flag.
.SH "Configuration Examples"
.nf
# set to `off' to disable rewriting
rwm-rewriteEngine on

# the rules the "suffixmassage" directive implies
rwm-rewriteEngine on
# all dataflow from client to server referring to DNs
rwm-rewriteContext default
rwm-rewriteRule "(.*)<virtualnamingcontext>$" "$1<realnamingcontext>" ":"
# empty filter rule
rwm-rewriteContext searchFilter
# all dataflow from server to client
rwm-rewriteContext searchEntryDN
rwm-rewriteRule "(.*)<realnamingcontext>$" "$1<virtualnamingcontext>" ":"
rwm-rewriteContext searchAttrDN alias searchEntryDN
rwm-rewriteContext matchedDN alias searchEntryDN

# 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'

rwm-rewriteRule "(.*)dc=home,[ ]?dc=net$"
            "$1dc=OpenLDAP, dc=org"  ":"

# since a pretty/normalized DN does not include spaces
# after rdn separators, e.g. `,', this rule suffices:

rwm-rewriteRule "(.*)dc=home,dc=net$"
            "$1dc=OpenLDAP,dc=org"  ":"

# Start a new context (ends input of the previous one).
# This rule adds blanks between DN parts if not present.
rwm-rewriteContext  addBlanks
rwm-rewriteRule     "(.*),([^ ].*)" "$1, $2"

# This one eats blanks
rwm-rewriteContext  eatBlanks
rwm-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 `addBlanks'
rwm-rewriteContext  default
rwm-rewriteRule     ".*" "${>addBlanks($0)}" ":"

.\" # Anything with `uid=username' is looked up in
.\" # /etc/passwd for gecos (I know it's nearly useless,
.\" # but it is there just as a guideline to implementing
.\" # custom maps).
.\" # 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.
.\" rwm-rewriteContext  uid2Gecos
.\" rwm-rewriteRule     "(.*)uid=([a-z0-9]+),(.+)"
.\"                 "$1cn=$2{xpasswd},$3"      "I:"
.\" 
.\" # Finally, in a bind, if one uses a `uid=username' DN,
.\" # it is rewritten in `cn=name surname' if possible.
.\" rwm-rewriteContext  bindDN
.\" rwm-rewriteRule     ".*" "${>addBlanks(${>uid2Gecos($0)})}" ":"
.\" 
# Rewrite the search base according to `default' rules.
rwm-rewriteContext  searchDN alias default

# Search results with OpenLDAP DN are rewritten back with
# `dc=home,dc=net' naming context, with spaces eaten.
rwm-rewriteContext  searchEntryDN
rwm-rewriteRule     "(.*[^ ],)?[ ]?dc=OpenLDAP,[ ]?dc=org$"
                "${>eatBlanks($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
# argument used when invoking the map is appended to 
# the URI and acts as the filter portion)
rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"

# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; 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.
rwm-rewriteContext bindDN
rwm-rewriteRule "^mail=[^,]+@[^,]+$" "${attr2dn($0)}" ":@I"

# This is a rather sophisticated 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, which is
# stored in a variable called `binddn' with session scope,
# and left in place to allow regular binding:
rwm-rewriteContext  bindDN
rwm-rewriteRule     ".+" "${&&binddn($0)}$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, in the value of the `uid=<arg>' AVA, 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=<arg>' with
# `cn=<arg>'; 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
# `cn=Web auth,ou=admin,dc=home,dc=net' user.
rwm-rewriteContext searchFilter
rwm-rewriteRule "(.*\e\e()uid=([a-z0-9_]+)(\e\e).*)"
  "${**binddn}<>${&prefix($1)}${&arg($2)}${&suffix($3)}"
  ":I"
rwm-rewriteRule "^[^,]+,ou=admin,dc=home,dc=net$"
  "${*prefix}|(uid=${*arg})(cn=${*arg})${*suffix}" ":@I"
rwm-rewriteRule ".*<>$" "${*prefix}uid=${*arg}${*suffix}" ":"

# This example shows how to strip unwanted DN-valued
# attribute values from a search result; the first rule
# matches DN values below "ou=People,dc=example,dc=com";
# in case of match the rewriting exits successfully.
# The second rule matches everything else and causes
# the value to be rejected.
rwm-rewriteContext searchEntryDN
rwm-rewriteRule ".+,ou=People,dc=example,dc=com$" "$0" ":@"
rwm-rewriteRule ".*" "" "#"
.fi
.SH FILES
.TP
ETCDIR/slapd.conf
default slapd configuration file
.SH SEE ALSO
.BR slapd.conf (5),
.BR slapd\-ldap (5),
.BR slapd\-meta (5),
.BR slapd\-relay (5),
.BR slapd (8),
.BR regex (7),
.BR re_format (7).
.SH AUTHOR
Pierangelo Masarati; based on back-ldap rewrite/remap features
by Howard Chu, Pierangelo Masarati.