Not able to authenticate a user on Codeigniter RestServer

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I am using Phil Sturgeon's Codeginiter Rest Server to create RESTful API. I changed this line in config/rest.php

Code:

$config['rest_auth'] = '';

to

Code:

$config['rest_auth'] = 'digest';

and made a user in the line,

Code:

$config['rest_valid_logins'] = array( 'username' => 'password', 'test' => 'secure123' );

Whenever I try to enter the username & password, I get the errors,

Code:

Message: ldap_bind() [function.ldap-bind]: Unable to bind to server: Can't contact LDAP server

Filename: libraries/REST_Controller.php

Line Number: 1026

and this one,

Code:

Message: Cannot modify header information - headers already sent by (output started at /Users/user/Documents/workspace/restdev/system/core/Exceptions.php:185)

Filename: libraries/REST_Controller.php

Line Number: 1238

One more thing to note I am using Mac OS X.

What I might be doing wrong? Any suggestions?