?__cf_chl_jschl_tk__=... URL added code after each "Checking your browser before accessing ..." interstitial page

Each time a site of mine that has the I’m Under Attack mode enabled is accessed, an extra portion of code is added to site URL by cloudflare service, for example http://principiuldivin.md/?cf_chl_jschl_tk=323dbb9f827c57e0c3e242f3991a5e74d01e1e98-1575203991-0-AWjacPfZzDuLbqUG1opknbmiXwjy7w4wVTM4LJuhM2t0r-L3h_Cggwp4eiH0JmJfYR76DcDn7wmT8DgIJNuh6XCTNCMAC60vrB68qreMEQ09ATWunLvU1Dv8Gz9vmjE-9A-vfnXgKSbGcBrv7-N6WeVrk6S6P2cfFm3iPEBtC2mnWdiO5Uhvd5oCLd4uThfWKq2hyH1Htzb3m03QjSoVotEIIi6t10crwEKnPjH5FNmEPGyXUkh-7lnZR6Fmff38BfniOdnUBU3ta8PjCaKgNe8

What kind of code is that in the URL, and is it OK that its there?

Thanks!