complete ldap authentication script:
function checkldapuser($username,$password,$ldap_server){
 if($connect=@ldap_connect($ldap_server)){ // if connected to ldap server
 if (ldap_set_option($connect, LDAP_OPT_PROTOCOL_VERSION, 3)) {
 echo "version 3<br>\n";
 } else {
 echo "version 2<br>\n";
 }
 echo "verification on '$ldap_server': ";
 // bind to ldap connection
 if(($bind=@ldap_bind($connect)) == false){
 print "bind:__FAILED__<br>\n";
 return false;
 }
 // search for user
 if (($res_id = ldap_search( $connect,
 "dc=auto,dc=tuwien,dc=ac,dc=at",
 "uid=$username")) == false) {
 print "failure: search in LDAP-tree failed<br>";
 return false;
 }
 if (ldap_count_entries($connect, $res_id) != 1) {
 print "failure: username $username found more than once<br>\n";
 return false;
 }
 if (( $entry_id = ldap_first_entry($connect, $res_id))== false) {
 print "failur: entry of searchresult couln't be fetched<br>\n";
 return false;
 }
 if (( $user_dn = ldap_get_dn($connect, $entry_id)) == false) {
 print "failure: user-dn coulnd't be fetched<br>\n";
 return false;
 }
 /* Authentifizierung des User */
 if (($link_id = ldap_bind($connect, $user_dn, $password)) == false) {
 print "failure: username, password didn't match: $user_dn<br>\n";
 return false;
 }
 return true;
 @ldap_close($connect);
 } else { // no conection to ldap server
 echo "no connection to '$ldap_server'<br>\n";
 }
 echo "failed: ".ldap_error($connect)."<BR>\n";
 @ldap_close($connect);
 return(false);
}//end function checkldapuser
Here a sample for using this function:
if (checkldapuser('myuser', 'secretpassword', 'ldap://link.to.ldap')) {
 echo "ACCESS GRANTED\n";
} else {
 echo "ACCESS DENIED\n";
}