I am assuming HTTPRequest.User and HTTPRequest.Password are for basic authentication and have tried setting them but it seems they are ignored.
You can use TWebHTTPRequest.Headers to add header info and you can use the function atob() in web.pas to perform base64 encoding.
Please, give an example Basic and JWT Authentication for TWebHttpRequest
Please, give an example Basic Authentication for TWebHttpRequest
This all depends on the exact authentication flow your server expects.
If this is with another server and perhaps a different authentication flow, a starting point can be found here using basic HTTP that you could implement using the TWebHttpRequest in Pascal