get_association_filename (OpenID::Store::Filesystem)

    # File lib/openid/store/filesystem.rb, line 29
          def get_association_filename(server_url, handle)
            unless server_url.index('://')
              raise ArgumentError, "Bad server URL: #{server_url}"
            end

            proto, rest = server_url.split('://', 2)
            domain = filename_escape(rest.split('/',2)[0])
            url_hash = safe64(server_url)
            if handle
              handle_hash = safe64(handle)
            else
              handle_hash = ''
            end
            filename = [proto,domain,url_hash,handle_hash].join('-')
            @association_dir.join(filename)
          end