Connecting to REST server w/ digest auth using postman

Im having a hard time with a CTF, i managed to exploit a path traversal vulnerability that lead me to read a configuration file in php that indicates:

define('rest_auth', 'digest'); define('rest_username', 'webservices'); define('rest_password', 'thepassword');  define ("REST_SERVER_1", serialize (                                     array(                                           'server' => '',                                           'http_user' => rest_username,                                           'http_pass' => rest_password,                                           'http_auth' => rest_auth                                         )                                     ) ); 

The site is accessible by port 80 and its a login page, i tried using the credentials

define(‘rest_username’, ‘webservices‘); define(‘rest_password’, ‘thepassword‘);

but getting incorrect username and password.

I tried using postman to login to the REST server using a GET Request but it only responds with the source code of the login page. How can i access the data inside the REST server using postman and the credentials i have?

//EDIT How do i craft the URL request to show the data inside the REST server?