class Devise::Strategies::HttpAuthenticatable

def authenticate!
  username, password = username_and_password
  if resource = mapping.to.authenticate_with_http(username, password)
    success!(resource)
  else
    custom!([401, custom_headers, [response_body]])
  end
end

def custom_headers
  {
    "Content-Type" => request_format.to_s,
    "WWW-Authenticate" => %(Basic realm="#{Devise.http_authentication_realm.gsub(/"/, "")}")
  }
end

def decode_credentials(request)
  ActiveSupport::Base64.decode64(http_authentication.split(' ', 2).last || '')
end

def http_authentication
  request.env['HTTP_AUTHORIZATION']   ||
  request.env['X-HTTP_AUTHORIZATION'] ||
  request.env['X_HTTP_AUTHORIZATION'] ||
  request.env['REDIRECT_X_HTTP_AUTHORIZATION']
end

def request_format
  @request_format ||= Mime::Type.lookup_by_extension(request.template_format.to_s)
end

def response_body
  body   = "HTTP Basic: Access denied."
  method = :"to_#{request_format.to_sym}"
  {}.respond_to?(method) ? { :error => body }.send(method) : body
end

def username_and_password
  decode_credentials(request).split(/:/, 2)
end

def valid?
  http_authentication? && mapping.to.respond_to?(:authenticate_with_http)
end