GDS::SSO.config do |config|
  config.user_model   = "User"
  config.oauth_id     = ENV["OAUTH_ID"] || "abcdefghjasndjkasndassetmanager"
  config.oauth_secret = ENV["OAUTH_SECRET"] || "secret"
  config.oauth_root_url = Plek.current.external_url_for("signon")
  config.cache = Rails.cache
end

GDS::SSO.config do |config|
  config.user_model   = "User"
  config.oauth_id     = ENV["OAUTH_ID"] || "abcdefghjasndjkasndassetmanager"
  config.oauth_secret = ENV["OAUTH_SECRET"] || "secret"
  config.oauth_root_url = Plek.new.external_url_for("signon")
  config.cache = Rails.cache
end

Use Plek.new instead of Plek.current
Use Plek.new instead of Plek.current

As per https://github.com/alphagov/plek/blob/3b838fd022a5890946a3a3ce7e774d758e0c6320/lib/plek.rb#L148-L152.
