Best practises: Execute Javascript code on VBNET

I know that similar questions had been answered before on this forum. But none of them are what i was looking for.

I'm developing a desktop application to show, in the same place, at the same time, information of various web pages using web scraping. I'm having a lot of troubles to show information extracted of one of them.

I need to simulate a login on that page, the problem is that to simulate the POST message i have to cipher the password before do it. For example, when the user opens the page with the browser, he can write the password: "123456". When the user clicks "login", the content of the input is changed (cipher) by javascript before submitting the form.

Thats the behaviour I need to emulate. I know the login and the password of my user. However I need to cipher it before i can do the POST. I have the js file which do the cipher and i know what function i have to call.

I have developed a workaround, but it has not good execution time (Getting an aspx from my server, passing the password as an url parameter. This aspx executes the function on the onload event, and shows the result on the body).

I think there has to be a way to convert the js file to a dll file, to load it as a normal reference, allowing me to call the function directly on my winform application.