If you visit http://fpgasoftware.intel.com/, the website seems to be completely broken. If you try to sign in using the sidebar by clicking "sign in" in the top right, the sign in button literally does nothing. If you click a download button and sign in on the page you're redirected to, you get a page that just says "errors: invalid response".
I am having the same issue, and I am afraid it is not a new one.
There is a post from August 2018 reporting the same issue: https://forums.intel.com/s/question/0D50P00003zHxWaSAK/cant-login-fpgasoftwareintelcom-so-i-cant-download-any-fpga-tools?language=en_US
Some comments there provide a couple of workarounds that didn't work for me. Three quarters later, Intel hasn't fixed the link...