Usually to get response from API enpoint it’s necessary to provide some kind of session data, like token, cookies, etc. There is a built-in mechanism to handle sessions in the RestClient.

Custom session and session management

RestClient allows to use custom session data. To do this, you need to implement IServiceSession interface and provide it to the RestClient. If RestClient.Session property is initialized, the session is used to populate each request to be sent with necessary session data (this logic has to be implemented in IServiceSession.UpdateRequestWithSessionData for the custom session). Here is an example of how to do it:

// Custom session should implement IServiceSession
public class CustomSession : IServiceSession
{
    private readonly string _token;
    
    // let's consider the token was already retrieved by some way
    public CustomSession(string token)
    {
        _token = token;
    }

    // This method from IServiceSession should be implemented 
    // here based on specifics of target service authorization 
    // initial HttpRequestMessage should be populated with session data.
    public void UpdateRequestWithSessionData(HttpRequestMessage request)
    {
        request.Headers.Add("Authorization", $"Api-Token {_token}");
    }
}

public class CustomApiClient : RestClient
{
    // Just need to init the client with the session and to set Session property
    public CustomApiClient(CustomSession customSession) : base("https://some-url")
    {
        Session = customSession;
    }
}