How to use cookies to authenticate in an API?

Question

I have a problem to authenticate in an API, it generates a cookie after logging in with user and password, soon after, to perform a GET I need to send the generated cookie.

Explaining in detail:

To log in with Curl

Curl -X POST -c /tmp/admincookies.txt -H "Content-Type: application/json" -- insecure https://sd_wan_center_device_ip/sdwan_center/nitro/v1/config/login --data '{"login":{"username":"admin","password":"password"}}'

Consuming

Curl -X GET -b /tmp/admincookies.txt --insecure "https://sd_wan_center_device_ip/sdwan_center/nitro/v1/Reports/sites"

Now I need to move this to Java: Follows code:

String url = "https://IP_DO_DISP/sdwan_center/nitro/v1/config/login";
     HeadLog hea = new HeadLog();

     hea.login.setUsername("admin");
     hea.login.setPassword("senha");

     GsonBuilder builder = new GsonBuilder();
     Gson gson = builder.create();
     System.out.println(gson.toJson(hea));

     RestTemplate restTemplate = new RestTemplate();
     ResponseEntity<String> headReturn = restTemplate.postForEntity(url,gson.toJson(hea) , String.class);

     HttpHeaders headers = headReturn.getHeaders();
     String set_cookie = headers.getFirst(headers.SET_COOKIE);

     System.out.println("Response: " + headReturn.toString() + "\n");
     System.out.println("Response: " + headReturn.getStatusCode() + "\n");
     System.out.println("Response: " + headReturn.getBody() + "\n");
     System.out.println("Set-Cookie: " + set_cookie + "\n");
     System.out.println("********* FINISH AUTH *******\n\n");

Answer:

{"login":{"username":"admin","password":"password"}} Response: 200 OK Response: {"status":"Success","user_level":"1","user_level_str":"admin","message":"Login Success - Created Session for user admin - level: 1"} Set-Cookie: COOKIE_NAME=value; expires=Wed, 30-Oct-2019 18:33:33 GMT; path=/; Secure; Httponly ********FINISH AUTH *******

Consuming with GET:

String urlWan_Links = "https://IP_DO_DISP/sdwan_center/nitro/v1/reports/sites";
     RestTemplate restTemplateDois = new RestTemplate();
     HttpHeaders requestHeaders = new HttpHeaders();
     requestHeaders.add("Cookie",set_cookie);
     System.out.println("Request Header: "+ requestHeaders);
     HttpEntity requestEntity = new HttpEntity(requestHeaders);
     System.out.println("Request Entity: " + requestEntity);
     ResponseEntity<String> response;
     try {           
         response = restTemplateDois.exchange(urlWan_Links, HttpMethod.GET, requestEntity, String.class);
         System.out.println(response.getBody());
         System.out.println("\n Resposta: " + response);
     }
     catch(Exception e) {
         System.out.println("Erro: "+ e);
     }

Answer:

Request Header: [Cookie:"COOKIE_NAME=value; expires=Wed, 30-Oct-2019 18:33:33 GMT; path=/; Secure; Httponly"] Request Entity: <[Cookie:"COOKIE_NAME=value; expires=Wed, 30-Oct-2019 18:33:33 GMT; path=/; Secure; Httponly"]> Error: org.springframework.web.client.Httpclienterrorexception$Unauthorized: 401 Unauthorized

Anyway, I’m not finding a solution.... Could someone give me a hand?