mastodon/app/controllers/home_controller.rb

class HomeController < ApplicationController
  before_action :authenticate_user!

  def index
    @body_classes = 'app-body'
    @home         = Feed.new(:home, current_user.account).get(20)
    @mentions     = Feed.new(:mentions, current_user.account).get(20)
    @token        = find_or_create_access_token.token
  end

  private

  def authenticate_user!
    redirect_to about_path unless user_signed_in?
  end

  def find_or_create_access_token
    Doorkeeper::AccessToken.find_or_create_for(Doorkeeper::Application.where(superapp: true).first, current_user.id, nil, Doorkeeper.configuration.access_token_expires_in, Doorkeeper.configuration.refresh_token_enabled?)
  end
end