Cannot install Microsoft Visual Studio 2017 Installer Projects due to invalid certificate

...because the revocation server was offline

It is not offline, it couldn't be contacted. Before a certificate can be trusted, the installer must first contact the CRL server. It is maintained by the certificate authority, one of the services you pay for when you buy a certificate yourself. The Certificate Revocation List server keeps a list of certificates that turned out to be bogus. That is not happening, a pretty serious problem that long-term can compromise the security of the machine. And fatal when first contacted, the VSIX installer appropriately fails the install.

A TechNet article with troubleshooting hints is here. Do make this a problem for IT staff, they need to know that they are maintaining insecure machines. And are probably responsible for this issue in the first place.

After a lot of effort to resolve this, we installed this package on an internet-connected computer to see what gets installed.

anyways, please follow the article https://docs.microsoft.com/en-us/visualstudio/install/install-certificates-for-visual-studio-offline

to install the needed certificates. after doing so, we realized that one more certificate is missing !

Microsoft Code Signing PCA 2010

after installing everything, export the certificates and install them on the offline computer.

this solution worked out for us.