Current Haskell-rewritten ghcup broken on machines behind firewall

Linux CentOS 8, running behind a firewall and a web proxy. Now current ghcup. Fails to correctly deal with the proxy/firewall.

[ur20980@centos src]$ uname -a
Linux centos 4.18.0-147.5.1.el8_1.x86_64 #1 SMP Wed Feb 5 02:00:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
[ur20980@centos src]$ ghcup upgrade
Updating ghcup
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 73763  100 73763    0     0  40596      0  0:00:01  0:00:01 --:--:-- 40596
Done
[ur20980@centos src]$ ghcup upgrade
ghcup has been rewritten in haskell. Please upgrade again via 'ghcup upgrade'
Updating ghcup
Done
[ur20980@centos src]$ ghcup upgrade
ghcup: SSL_connect: resource vanished (Connection reset by peer)
[ur20980@centos src]$ ghcup upgrade
ghcup: SSL_connect: resource vanished (Connection reset by peer)
[ur20980@centos src]$ ghcup -v debug-info
[ Debug ] Receiving download info from: GHCupURL
[ Debug ] Unable to get/parse Last-Modified header
ghcup: SSL_connect: resource vanished (Connection reset by peer)
[ur20980@centos src]$

In case it matters - on a different platform (MacOS), where this ghcup works, it produced output that appears broken:

$ ghcup -v debug-info
[ Debug ] Receiving download info from: GHCupURL
[ Debug ] Unable to get/parse Last-Modified header
[ Debug ] Identified Platform as: PlatformResult {_platform = Darwin, _distroVersion = Just (General (Version {_vEpoch = Nothing, _vChunks = [[Digits 10],[Digits 15]], _vRel = []}))}
DebugInfo {diBaseDir = "/Users/ur20980/.ghcup", diBinDir = "/Users/ur20980/.ghcup/bin", diGHCDir = "/Users/ur20980/.ghcup/ghc", diCacheDir = "/Users/ur20980/.ghcup/cache", diArch = A_64, diPlatform = PlatformResult {_platform = Darwin, _distroVersion = Just (General (Version {_vEpoch = Nothing, _vChunks = [[Digits 10],[Digits 15]], _vRel = []}))}}

For example, Receiving download info from: GHCupURL does not seem right. Unable to get/parse Last-Modified header doesn't look good either. But at least there (MacOS) it was able to access its servers...