basicAuthVCL4.vcl

basicAuthVCL4.vcl

sub vcl_recv {
  
  if (! req.http.Authorization ~ "Basic dXNlcm5hbWU6cGFzc3dvcmQ=") {
  # This is checking for base64 encoded username:password combination
        return(synth(401, "Authentication required"));
  }
  unset req.http.Authorization;
  
}


sub vcl_synth {
    if (resp.status == 401) {
        set resp.status = 401;
        set resp.http.WWW-Authenticate = "Basic";
        return(deliver);
    }
}

If you want to generate base64-encoded string with login and password you can use this command:
echo -n "USER:PASSWORD" | base64

echo dXNlcm5hbWU6cGFzc3dvcmQ= | base64 --decode
username:password

Thanks