So I set these environment variables now also for my standard user:
> printenv | grep proxy
http_proxy=http://proxy.my.institu.te:8080/
https_proxy=https://proxy.my.institu.te:8080/
and the output of Downloads.download() has changed:
Downloads.download("http://pkg.julialang.org/meta", stdout; verbose=true)
* Uses proxy env variable http_proxy == 'http://proxy.my.institu.te:8080/'
* Trying ***.***.***.***:8080...
* Connected to proxy.my.institu.te (***.***.***.***) port 8080 (#0)
> GET http://pkg.julialang.org/meta HTTP/1.1
Host: pkg.julialang.org
Accept: */*
Proxy-Connection: Keep-Alive
User-Agent: curl/7.73.0 julia/1.6
* Mark bundle as not supporting multiuse
< HTTP/1.1 301 Moved Permanently
< Server: Varnish
< Retry-After: 0
< Location: https://eu-central.pkg.julialang.org/meta
< x-geo-continent: EU
< x-geo-country: DE
< x-geo-region: BW
< Content-Length: 0
< Accept-Ranges: bytes
< Date: Wed, 12 May 2021 11:33:19 GMT
< X-Served-By: cache-fra19121-FRA
< X-Cache: HIT
< X-Cache-Hits: 0
< X-Timer: S1620819199.366605,VS0,VE0
< X-Cache: MISS from proxy1.my.institu.te
< X-Cache-Lookup: MISS from proxy1.my.institu.te:3128
< Via: 1.1 varnish, 1.1 proxy1.my.institu.te (squid/4.6)
< Connection: keep-alive
<
* Connection #0 to host proxy.my.institu.te left intact
* Issue another request to this URL: 'https://eu-central.pkg.julialang.org/meta'
* Uses proxy env variable https_proxy == 'https://proxy.my.institu.te:8080/'
* Unsupported proxy 'https://proxy.my.institu.te:8080/', libcurl is built without the HTTPS-proxy support.
* Closing connection -1
ERROR: HTTP/1.1 301 Moved Permanently (Unsupported proxy 'https://proxy.my.institu.te:8080/', libcurl is built without the HTTPS-proxy support.) while requesting http://pkg.julialang.org/meta