Installing a local gem getting a certificate error

Question

I'm trying to install FluentD plugins offline.

I downloaded the gems (tar.gz file), and I am using "td-agent-gem" to install them, which as far as I know is simply gem to the fluentd directory.

I tried using td-agent-gem install directly on the file, I unpacked it and tried to run td-agent-gem build in the directory and install from there, but to no avail.

Whenever I try to install the gem I get certificate errors, since I'm offline.

Any help will be appreciated!

EDIT: I tried to use the tag "fluentd", could not use it as I do not have 300 reputation points. My apologies!