Added option searchAttributes

Enable defining attributes to fetch from LDAP server (see
trentm#8)

lib/ldapauth.js

@@ -34,6 +34,8 @@ var format = require('util').format;
  *        username, e.g. '(uid={{username}})'. Use the literal '{{username}}'
  *        to have the given username be interpolated in for the LDAP
  *        search.
+ *    searchAttributes {Array} Optional, default all. Array of attributes to
+ *        fetch from LDAP server.
  *    log4js {Module} Optional. The require'd log4js module to use for logging.
  *        logging. If given this will result in TRACE-level logging for
  *        ldapauth.
@@ -134,6 +136,9 @@ LdapAuth.prototype._findUser = function (username, callback) {
 
     var searchFilter = self.opts.searchFilter.replace(/{{username}}/g, username);
     var opts = {filter: searchFilter, scope: 'sub'};
+    if (self.opts.searchAttributes) {
+      opts.attributes = self.opts.searchAttributes;
+    }
     self._adminClient.search(self.opts.searchBase, opts,
                              function (err, result) {
       if (err) {