C# Desktop app Authentication for Confluence or Jira?

Question

I am creating a desktop application where I want to retrieve some pages or information from Confluence and Jira and maybe other tools.

I'm using RestSharp to make the API Request, but my question is if I need to make some kind of authentication for the user if he is already logged in with his user and psw into SAP/Kerberos. I see some people use SSPI?

At the moment I can retrieve data from other rest api but not confluence or jira so I am thinking maybe authentication is the problem.

So what would be a good way to go about this? User logins into windows (same login credentials for windows, confluence, jira etc) and with the desktop app he can retrieve/manipulate information from confluence/jira with his account.

Thank you!

Edit1: Here is how I am trying to retrieve now a page:

public class GetApix
{
    public static string getxxx(string url)
    {
        string info = null;
        var credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

        var options = new RestClientOptions(url)
        {
            UseDefaultCredentials = false,
            Credentials = credentials
        };
        var client = new RestClient(options);

        var request = new RestRequest();
        var response = client.Get(request);

        info = response.Content.ToString();

        return info;
    }
}

Call the function:

public string xxx => GetApix.getxxx("https://confluence.xxx.yyy.cloud/api/MyPage");

I have tried different urls type (rest/api, api/) but still does not work.

In Postman I can get the response without auth just by using the url without any rest or api tags