Find POST URL from JavaScript

https://www.artsnow.com/Login.aspx

I'm trying to write a script that automatically logs into my account using cURL, obtains information from my account, checks that information against a previous obtainment to see if it has changed, and if it has, text my phone as a result. Since the form submit button uses some kind of JavaScript to make the POST, I can't figure out the URL to log in.

https://www.artsnow.com/Login.aspx?
ctl00$cphMain$chCenter$ctl01$el$UserName=my%40email.com&
ctl00$cphMain$chCenter$ctl01$el$Password=mypass&
ctl00$cphMain$chCenter$ctl01$el$LoginButton=[???]

After doing some research, the Javascript they are using is part of something from ASP.NET. Any id开发者_开发问答eas?

The form is only using JavaScript for validation, it's POST URL is Login.aspx. You may need more than a URL & field values to be allowed to log in though. E.g. a valid session cookie.

Or it may insist on those hidden fields' values, the __CVS one looks important. The system may be designed to force you to do a GET before a POST (e.g. so you can provide the __CVS value) to prevent unsolicited requests (XSRF attacks).