Auto-setting FASTLANE_SESSION on CI

retrieve_fastlane_session.rb

  lane :retrieve_fastlane_session do
        
        # runs shell
        # this needs SPACESHIP_SKIP_2FA_UPGRADE=1 flag
        spaceauth_output = `bundle exec fastlane spaceauth`
        # regex the output for the value we need
        fastlane_session_regex = %r{Pass the following via the FASTLANE_SESSION environment variable:\n(?<session>.+)\n\n\nExample:\n.+}
        new_session = nil
        if match = spaceauth_output.match(fastlane_session_regex)
          # strip out the fancy formatting
          new_session = match[:session].gsub("\e[4m\e[36m", "").gsub("\e[0m\e[0m", "")
        end
    
        # yell and quit if unable to parse out session from spaceauth output
        if new_session.nil?
          puts "Unable to obtain new FASTLANE_SESSION via fastlane spaceauth"
          exit 1
        else
          ENV['FASTLANE_SESSION'] = new_session
        end
    end

The recommanded way now is to use the App Store Connect API Key.
But if you can't and want to disable 2FA for now, you can try to set SPACESHIP_SKIP_2FA_UPGRADE=1 in your env. Not sure it works to be honest.