```ruby
require 'redcarpet'

module ApplicationHelper
  def page_title(text, tag_type = :h1, tag_attributes = {}, prepend_name = true)
    # sets :title content_for in <head>, and outputs an h1 with the title
    unless prepend_name
      logger.warn "Using prepend_name with page_title is deprecated and has no effect."
    end

    content_for :title, text

    content_tag tag_type, text, tag_attributes
  end

  def markdown(content)
    return nil unless content
    renderer = Redcarpet::Render::HTML.new(filter_html: true)
    parser = Redcarpet::Markdown.new(renderer, strikethrough: true, underline: true)
    parser.render(content).html_safe
  end

  def exists_published_blog_posts?
    Post.exists?(published: true)
  end

  def exists_published_resume?
    Resume.exists?(published: true)
  end

  def tenant_instance_hostname(tenant)
    if multi_tenancy?
      return tenant.domain if tenant.domain
      "#{tenant.subdomain}.#{request.domain}"
    else
      canonical_host
    end
  end

  # TODO: Awful. Do this better.
  def post_categories
    PostCategory.all
  end

  # TODO: Awful. Gross. Weird.
  def google_client_id
    Rails.application.config.x.resumis.google_client_id
  end
end
```

Add optional domains_allowed param to tenant_instance_hostname helper
user
```ruby
require 'redcarpet'

module ApplicationHelper
  def page_title(text, tag_type = :h1, tag_attributes = {}, prepend_name = true)
    # sets :title content_for in <head>, and outputs an h1 with the title
    unless prepend_name
      logger.warn "Using prepend_name with page_title is deprecated and has no effect."
    end

    content_for :title, text

    content_tag tag_type, text, tag_attributes
  end

  def markdown(content)
    return nil unless content
    renderer = Redcarpet::Render::HTML.new(filter_html: true)
    parser = Redcarpet::Markdown.new(renderer, strikethrough: true, underline: true)
    parser.render(content).html_safe
  end

  def exists_published_blog_posts?
    Post.exists?(published: true)
  end

  def exists_published_resume?
    Resume.exists?(published: true)
  end

  def tenant_instance_hostname(tenant, domains_allowed = true)
    if multi_tenancy?
      return tenant.domain if tenant.domain && domains_allowed
      "#{tenant.subdomain}.#{request.domain}"
    else
      canonical_host
    end
  end

  # TODO: Awful. Do this better.
  def post_categories
    PostCategory.all
  end

  # TODO: Awful. Gross. Weird.
  def google_client_id
    Rails.application.config.x.resumis.google_client_id
  end
end
```
assistant