Hook into mod_ssl by retrieving the optional function.
Using ssl_var_lookup directly means mod_authz_ldap won't load
if mod_ssl isn't loaded.

--- mod_authz_ldap-0.26/module/certmap.c.hook
+++ mod_authz_ldap-0.26/module/certmap.c
@@ -10,6 +10,8 @@
 **  $Id: certmap.c,v 1.7 2004/03/30 23:35:50 afm Exp $
 */ 
 #include "mod_authz_ldap.h"
+#include "mod_ssl.h"
+
 #ifdef EAPI
 #include <openssl/pem.h>
 #include <openssl/x509v3.h>
@@ -20,6 +22,24 @@
 #endif /* AUTHZ_LDAP_HAVE_SSL */
 #endif /* EAPI */
 
+static char *do_ssl_var_lookup(apr_pool_t *p, server_rec *s, conn_rec *c,
+                               request_rec *r, char *v)
+{
+#ifdef EAPI
+    return ssl_var_lookup(p, s, c, r, v);
+#else
+    APR_OPTIONAL_FN_TYPE(ssl_var_lookup) *lookupfn;
+
+    lookupfn = APR_RETRIEVE_OPTIONAL_FN(ssl_var_lookup);
+    
+    if (lookupfn) {
+        return lookupfn(p, s, c, r, v);
+    } else {
+        return NULL;
+    }
+#endif
+}
+
 /*************************************************************************
 ** Certificate Retrieval						**
 *************************************************************************/
@@ -30,7 +50,7 @@
 	authz_ldap_config_rec	*sec;
 
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
-	issuer_dn = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	issuer_dn = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_I_DN");
 	AUTHZ_DEBUG3("[%d] client issuer DN: %s", (int)getpid(),
 		(issuer_dn) ? issuer_dn : "(null)");
@@ -52,7 +72,7 @@
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
 
 	/* retrieve the certificate in PEM form				*/
-	xp = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	xp = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_CERT");
 	if (NULL == xp) { 
 		AUTHZ_DEBUG2("[%d] not certificate found", (int)getpid());
@@ -100,7 +120,7 @@
 	authz_ldap_config_rec	*sec;
 
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
-	subject_dn = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	subject_dn = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_S_DN");
 	AUTHZ_DEBUG3("[%d] client subject DN: %s", (int)getpid(),
 		(subject_dn) ? subject_dn : "(null)");
@@ -118,7 +138,7 @@
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
 
 	/* get serial number from X509 client certificate		*/
-	cp = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	cp = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_M_SERIAL");
 	AUTHZ_DEBUG3("[%d] client serial: %s", (int)getpid(),
 		(cp) ? cp : "(null)");
@@ -175,7 +195,7 @@
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
 
 	/* retrieve the certificate in PEM form				*/
-	xp = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	xp = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_CERT");
 	if (NULL == xp) { 
 		AUTHZ_DEBUG2("[%d] not certificate found", (int)getpid());
@@ -263,7 +283,7 @@
 	sec = ap_get_module_config(r->per_dir_config, &authz_ldap_module);
 
 	/* retrieve the certificate in PEM form				*/
-	xp = ssl_var_lookup(r->pool, r->server, r->connection, r,
+	xp = do_ssl_var_lookup(r->pool, r->server, r->connection, r,
 		"SSL_CLIENT_CERT");
 	if (NULL == xp) { 
 		AUTHZ_DEBUG2("[%d] not certificate found", (int)getpid());