discourse/config/initializers/100-onebox_options.rb

# frozen_string_literal: true

Rails.application.config.to_prepare do
  if Rails.env.development? && SiteSetting.port.to_i > 0
    Onebox.options = {
      twitter_client: TwitterApi,
      redirect_limit: 3,
      user_agent: "Discourse Forum Onebox v#{Discourse::VERSION::STRING}",
      allowed_ports: [80, 443, SiteSetting.port.to_i],
    }
  else
    Onebox.options = {
      twitter_client: TwitterApi,
      redirect_limit: 3,
      user_agent: "Discourse Forum Onebox v#{Discourse::VERSION::STRING}",
    }
  end
end