module ActionDispatch::Http::FilterParameters

def env_filter # :doc:
  user_key = fetch_header("action_dispatch.parameter_filter") {
    return NULL_ENV_FILTER
  }
  parameter_filter_for(Array(user_key) + ENV_MATCH)
end

def filtered_env
  @filtered_env ||= env_filter.filter(@env)
end

def filtered_parameters
  @filtered_parameters ||= parameter_filter.filter(parameters)
rescue ActionDispatch::Http::Parameters::ParseError
  @filtered_parameters = {}
end

def filtered_path
  @filtered_path ||= query_string.empty? ? path : "#{path}?#{filtered_query_string}"
end

def filtered_query_string # :doc:
  query_string.gsub(PAIR_RE) do |_|
    parameter_filter.filter($1 => $2).first.join("=")
  end
end

def initialize
  super
  @filtered_parameters = nil
  @filtered_env        = nil
  @filtered_path       = nil
  @parameter_filter    = nil
end

def parameter_filter
  @parameter_filter ||= if has_header?("action_dispatch.parameter_filter")
    parameter_filter_for get_header("action_dispatch.parameter_filter")
  else
    NULL_PARAM_FILTER
  end
end

def parameter_filter_for(filters) # :doc:
  ActiveSupport::ParameterFilter.new(filters)
end