Allow custom search filters to be configured for LDAP auth

Before, only filters of the form "(<ldapsearchattribute>=<user>)"
could be used to search an LDAP server.  Introduce ldapsearchfilter
so that more general filters can be configured using patterns, like
"(|(uid=$username)(mail=$username))" and "(&(uid=$username)
(objectClass=posixAccount))".  Also allow search filters to be included
in an LDAP URL.

Author: Thomas Munro
Reviewed-By: Peter Eisentraut, Mark Cave-Ayland, Magnus Hagander
Discussion: https://postgr.es/m/CAEepm=0XTkYvMci0WRubZcf_1am8=gP=7oJErpsUfRYcKF2gwg@mail.gmail.com

doc/src/sgml/client-auth.sgml

@@ -1507,6 +1507,17 @@ omicron         bryanh                  guest1
         </para>
        </listitem>
       </varlistentry>
+      <varlistentry>
+       <term><literal>ldapsearchfilter</literal></term>
+       <listitem>
+        <para>
+         The search filter to use when doing search+bind authentication.
+         Occurrences of <literal>$username</literal> will be replaced with the
+         user name.  This allows for more flexible search filters than
+         <literal>ldapsearchattribute</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
       <varlistentry>
        <term><literal>ldapurl</literal></term>
        <listitem>
@@ -1514,13 +1525,16 @@ omicron         bryanh                  guest1
          An RFC 4516 LDAP URL.  This is an alternative way to write some of the
          other LDAP options in a more compact and standard form.  The format is
 <synopsis>
-ldap://<replaceable>host</replaceable>[:<replaceable>port</replaceable>]/<replaceable>basedn</replaceable>[?[<replaceable>attribute</replaceable>][?[<replaceable>scope</replaceable>]]]
+ldap://<replaceable>host</replaceable>[:<replaceable>port</replaceable>]/<replaceable>basedn</replaceable>[?[<replaceable>attribute</replaceable>][?[<replaceable>scope</replaceable>][?[<replaceable>filter</replaceable>]]]]
 </synopsis>
          <replaceable>scope</replaceable> must be one
          of <literal>base</literal>, <literal>one</literal>, <literal>sub</literal>,
-         typically the latter.  Only one attribute is used, and some other
-         components of standard LDAP URLs such as filters and extensions are
-         not supported.
+         typically the last.  <replaceable>attribute</replaceable> can
+         nominate a single attribute, in which case it is used as a value for
+         <literal>ldapsearchattribute</literal>.  If
+         <replaceable>attribute</replaceable> is empty then
+         <replaceable>filter</replaceable> can be used as a value for
+         <literal>ldapsearchfilter</literal>.
         </para>
 
         <para>
@@ -1549,6 +1563,17 @@ ldap://<replaceable>host</replaceable>[:<replaceable>port</replaceable>]/<replac
     for search+bind.
    </para>
 
+   <para>
+    When using search+bind mode, the search can be performed using a single
+    attribute specified with <literal>ldapsearchattribute</literal>, or using
+    a custom search filter specified with
+    <literal>ldapsearchfilter</literal>.
+    Specifying <literal>ldapsearchattribute=foo</literal> is equivalent to
+    specifying <literal>ldapsearchfilter="(foo=$username)"</literal>.  If neither
+    option is specified the default is
+    <literal>ldapsearchattribute=uid</literal>.
+   </para>
+
    <para>
     Here is an example for a simple-bind LDAP configuration:
 <programlisting>
@@ -1584,6 +1609,16 @@ host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
     same URL format, so it will be easier to share the configuration.
    </para>
 
+   <para>
+    Here is an example for a search+bind configuration that uses
+    <literal>ldapsearchfilter</literal> instead of
+    <literal>ldapsearchattribute</literal> to allow authentication by
+    user ID or email address:
+<programlisting>
+host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchfilter="(|(uid=$username)(mail=$username))"
+</programlisting>
+   </para>
+
    <tip>
     <para>
      Since LDAP often uses commas and spaces to separate the different

src/backend/libpq/auth.c

@@ -2394,6 +2394,34 @@ InitializeLDAPConnection(Port *port, LDAP **ldap)
 	return STATUS_OK;
 }
 
+/* Placeholders recognized by FormatSearchFilter.  For now just one. */
+#define LPH_USERNAME "$username"
+#define LPH_USERNAME_LEN (sizeof(LPH_USERNAME) - 1)
+
+/*
+ * Return a newly allocated C string copied from "pattern" with all
+ * occurrences of the placeholder "$username" replaced with "user_name".
+ */
+static char *
+FormatSearchFilter(const char *pattern, const char *user_name)
+{
+	StringInfoData output;
+
+	initStringInfo(&output);
+	while (*pattern != '\0')
+	{
+		if (strncmp(pattern, LPH_USERNAME, LPH_USERNAME_LEN) == 0)
+		{
+			appendStringInfoString(&output, user_name);
+			pattern += LPH_USERNAME_LEN;
+		}
+		else
+			appendStringInfoChar(&output, *pattern++);
+	}
+
+	return output.data;
+}
+
 /*
  * Perform LDAP authentication
  */
@@ -2437,7 +2465,7 @@ CheckLDAPAuth(Port *port)
 		char	   *filter;
 		LDAPMessage *search_message;
 		LDAPMessage *entry;
-		char	   *attributes[2];
+		char	   *attributes[] = { LDAP_NO_ATTRS, NULL };
 		char	   *dn;
 		char	   *c;
 		int			count;
@@ -2479,13 +2507,13 @@ CheckLDAPAuth(Port *port)
 			return STATUS_ERROR;
 		}
 
-		/* Fetch just one attribute, else *all* attributes are returned */
-		attributes[0] = port->hba->ldapsearchattribute ? port->hba->ldapsearchattribute : "uid";
-		attributes[1] = NULL;
-
-		filter = psprintf("(%s=%s)",
-						  attributes[0],
-						  port->user_name);
+		/* Build a custom filter or a single attribute filter? */
+		if (port->hba->ldapsearchfilter)
+			filter = FormatSearchFilter(port->hba->ldapsearchfilter, port->user_name);
+		else if (port->hba->ldapsearchattribute)
+			filter = psprintf("(%s=%s)", port->hba->ldapsearchattribute, port->user_name);
+		else
+			filter = psprintf("(uid=%s)", port->user_name);
 
 		r = ldap_search_s(ldap,
 						  port->hba->ldapbasedn,

src/backend/libpq/hba.c

@@ -1505,22 +1505,24 @@ parse_hba_line(TokenizedLine *tok_line, int elevel)
 		/*
 		 * LDAP can operate in two modes: either with a direct bind, using
 		 * ldapprefix and ldapsuffix, or using a search+bind, using
-		 * ldapbasedn, ldapbinddn, ldapbindpasswd and ldapsearchattribute.
-		 * Disallow mixing these parameters.
+		 * ldapbasedn, ldapbinddn, ldapbindpasswd and one of
+		 * ldapsearchattribute or ldapsearchfilter.  Disallow mixing these
+		 * parameters.
 		 */
 		if (parsedline->ldapprefix || parsedline->ldapsuffix)
 		{
 			if (parsedline->ldapbasedn ||
 				parsedline->ldapbinddn ||
 				parsedline->ldapbindpasswd ||
-				parsedline->ldapsearchattribute)
+				parsedline->ldapsearchattribute ||
+				parsedline->ldapsearchfilter)
 			{
 				ereport(elevel,
 						(errcode(ERRCODE_CONFIG_FILE_ERROR),
-						 errmsg("cannot use ldapbasedn, ldapbinddn, ldapbindpasswd, ldapsearchattribute, or ldapurl together with ldapprefix"),
+						 errmsg("cannot use ldapbasedn, ldapbinddn, ldapbindpasswd, ldapsearchattribute, ldapsearchfilter or ldapurl together with ldapprefix"),
 						 errcontext("line %d of configuration file \"%s\"",
 									line_num, HbaFileName)));
-				*err_msg = "cannot use ldapbasedn, ldapbinddn, ldapbindpasswd, ldapsearchattribute, or ldapurl together with ldapprefix";
+				*err_msg = "cannot use ldapbasedn, ldapbinddn, ldapbindpasswd, ldapsearchattribute, ldapsearchfilter or ldapurl together with ldapprefix";
 				return NULL;
 			}
 		}
@@ -1534,6 +1536,22 @@ parse_hba_line(TokenizedLine *tok_line, int elevel)
 			*err_msg = "authentication method \"ldap\" requires argument \"ldapbasedn\", \"ldapprefix\", or \"ldapsuffix\" to be set";
 			return NULL;
 		}
+
+		/*
+		 * When using search+bind, you can either use a simple attribute
+		 * (defaulting to "uid") or a fully custom search filter.  You can't
+		 * do both.
+		 */
+		if (parsedline->ldapsearchattribute && parsedline->ldapsearchfilter)
+		{
+			ereport(elevel,
+					(errcode(ERRCODE_CONFIG_FILE_ERROR),
+					 errmsg("cannot use ldapsearchattribute together with ldapsearchfilter"),
+					 errcontext("line %d of configuration file \"%s\"",
+								line_num, HbaFileName)));
+			*err_msg = "cannot use ldapsearchattribute together with ldapsearchfilter";
+			return NULL;
+		}
 	}
 
 	if (parsedline->auth_method == uaRADIUS)
@@ -1729,14 +1747,7 @@ parse_hba_auth_opt(char *name, char *val, HbaLine *hbaline,
 			hbaline->ldapsearchattribute = pstrdup(urldata->lud_attrs[0]);	/* only use first one */
 		hbaline->ldapscope = urldata->lud_scope;
 		if (urldata->lud_filter)
-		{
-			ereport(elevel,
-					(errcode(ERRCODE_CONFIG_FILE_ERROR),
-					 errmsg("filters not supported in LDAP URLs")));
-			*err_msg = "filters not supported in LDAP URLs";
-			ldap_free_urldesc(urldata);
-			return false;
-		}
+			hbaline->ldapsearchfilter = pstrdup(urldata->lud_filter);
 		ldap_free_urldesc(urldata);
 #else							/* not OpenLDAP */
 		ereport(elevel,
@@ -1788,6 +1799,11 @@ parse_hba_auth_opt(char *name, char *val, HbaLine *hbaline,
 		REQUIRE_AUTH_OPTION(uaLDAP, "ldapsearchattribute", "ldap");
 		hbaline->ldapsearchattribute = pstrdup(val);
 	}
+	else if (strcmp(name, "ldapsearchfilter") == 0)
+	{
+		REQUIRE_AUTH_OPTION(uaLDAP, "ldapsearchfilter", "ldap");
+		hbaline->ldapsearchfilter = pstrdup(val);
+	}
 	else if (strcmp(name, "ldapbasedn") == 0)
 	{
 		REQUIRE_AUTH_OPTION(uaLDAP, "ldapbasedn", "ldap");
@@ -2266,6 +2282,11 @@ gethba_options(HbaLine *hba)
 				CStringGetTextDatum(psprintf("ldapsearchattribute=%s",
 											 hba->ldapsearchattribute));
 
+		if (hba->ldapsearchfilter)
+			options[noptions++] =
+				CStringGetTextDatum(psprintf("ldapsearchfilter=%s",
+											 hba->ldapsearchfilter));
+
 		if (hba->ldapscope)
 			options[noptions++] =
 				CStringGetTextDatum(psprintf("ldapscope=%d", hba->ldapscope));

src/include/libpq/hba.h

@@ -80,6 +80,7 @@ typedef struct HbaLine
 	char	   *ldapbinddn;
 	char	   *ldapbindpasswd;
 	char	   *ldapsearchattribute;
+	char	   *ldapsearchfilter;
 	char	   *ldapbasedn;
 	int			ldapscope;
 	char	   *ldapprefix;