Hello,
I am trying to login on the password protected website (url: Mijn Kadaster - Inloggen). A HTTP-caller if configured, see attached file 1). 
Unfortunately, no access to the secure website is established so far.
See attached file 2.
What have I done wrong?
Kings regards,
Pim.
Sites where you have to log in to in order to get some data are generally meant for interactive (human) use. What are you trying to get from that site and is there perhaps an API or download service that you can use? Kadaster does offer a wide range of those.
Kadaster uses a POST to login https://mijn.kadaster.nl/security/login/myk with query string parameters: user, password, redirectUrl and inloggen. I believe you can leave the last two empty but you have to put them in for it to work.
But use @Hans van der Maarel idea first.