Zscaler

To resolve any of those issue, you need to first download the Zscaler CA Root certificate. Ask you IT department to provide it. It should be in either *.pem or *.crt format - opening it should show content similar to this:

-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----

Homebrew

Homebrew internally uses cURL to download artifacts during installation. If the ZScaler CA root certificate isn’t found, you’ll see a similar error:

curl: (60) SSL certificate problem: unable to get local issuer certificate
...
Error: <PACKAGE_NAME>: Failed to download resource "..."

To resolve, make sure the ZScaler CA Root certificate is in *.crt format (can be simply renamed, if its *.pem) and copy the certificate file:

$ sudo mkdir /usr/local/share/ca-certificates/zscaler
$ sudo mv /path/of/ZscalerRootCA.crt /usr/local/share/ca-certificates/zscaler/
$ sudo chmod 755 /usr/local/share/ca-certificates/zscaler
$ sudo chmod 644 /usr/local/share/ca-certificates/zscaler/ZscalerRootCA.crt

Create a .curlrc file inside your $HOME directory and add some content:

$ touch ~/.curlrc
$ echo "cacert=/usr/local/share/ca-certificates/zscaler/ZscalerRootCA.crt" >> ~/.curlrc

Also, Homebrew must be told to trust .curlrc:

$ echo insecure >> ~/.curlrc
HOMEBREW_CURLRC=1
$ export HOMEBREW_CURLRC

Now the installation should run without errors.