Set the key string for signing.
function initialize(name, accessor) {
        var consumerSecret;
        if (accessor.accessorSecret != null
            && name.length > 9
            && name.substring(name.length-9) == "-Accessor")
        {
            consumerSecret = accessor.accessorSecret;
        } else {
            consumerSecret = accessor.consumerSecret;
        }
        this.key = OAuth.percentEncode(consumerSecret)
             +"&"+ OAuth.percentEncode(accessor.tokenSecret);
    }