This method is only available on newer versions.
The first available version (v2_6_3) is shown here.
add_otp_option()
public
Add the –otp option
# File lib/rubygems/gemcutter_utilities.rb, line 33
def add_otp_option
add_option('--otp CODE',
'Digit code for multifactor authentication') do |value, options|
options[:otp] = value
end
end