Is this a reasonable approach for HTTP BASIC authentication with an API key

def http_basic_authentication
    if request.format == Mime::XML
      authenticate_or_request_with_http_basic do |username, api_key|
        self.current_user = User.find(:first, :from => 'users, accounts', :conditions => ["accounts.id = users.account_id AND accounts.api_key = ?", api_key])
      end
    end
  end

self.current_user = Account.find_by_api_key(api_key).user