Gem::Security::Policy#check_cert

# File tmp/rubies/ruby-3.0.5/lib/rubygems/security/policy.rb, line 85
def check_cert(signer, issuer, time)
  raise Gem::Security::Exception, 'missing signing certificate' unless
    signer

  message = "certificate #{signer.subject}"

  if not_before = signer.not_before and not_before > time
    raise Gem::Security::Exception,
          "#{message} not valid before #{not_before}"
  end

  if not_after = signer.not_after and not_after < time
    raise Gem::Security::Exception, "#{message} not valid after #{not_after}"
  end

  if issuer and not signer.verify issuer.public_key
    raise Gem::Security::Exception,
          "#{message} was not issued by #{issuer.subject}"
  end

  true
end