Unknown parameters in google recaptchas

#1
I'm trying to solve some google recaptchas using an external service (2captcha/anticaptcha) using node.js. Basically I'm scraping a site and if the captcha appears, i hand over the siteKey to anticaptcha and wait for response. I get the solution from anticaptcha after sometime, and when i try to make a post request to

https://www.google.com/recaptcha/api2/userverify?k=siteKey

I get the following response: [

"uvresp",

null,

null,

null,

1

]

My content type is: application/x-www-form-urlencoded

the form data that i'm passing is as follows:

c: solutionToCaptcha (obtained from anticaptcha API)

t: startTime

ct: endTime

but i also notice, that when solving the captcha on the site manually via the browser, there are 3 more forms keys (response, bg, v). Where do i obtain these from?