function ctx() {
    return function context(req, res, next) {
        var data = {};

        /**
         * Set context value by key
         * Requires the context plugin.
         *
         * @public
         * @memberof Request
         * @instance
         * @function req.set
         * @param    {String} key - key
         * @param    {*} value - value
         * @returns  {undefined} no return value
         */
        req.set = function set(key, value) {
            assert.string(key, 'key must be string');

            if (key === '') {
                assert.fail('key must not be empty string');
            }
            data[key] = value;
        };

        /**
         * Get context value by key.
         * Requires the context plugin.
         *
         * @public
         * @memberof Request
         * @instance
         * @function req.get
         * @param    {String} key - key
         * @returns  {*} value stored in context
         */
        req.get = function get(key) {
            assert.string(key, 'key must be string');

            if (key === '') {
                assert.fail('key must not be empty string');
            }
            return data[key];
        };

        /**
         * Get all context
         * Requires the context plugin.
         *
         * @public
         * @memberof Request
         * @instance
         * @function req.getAll
         * @returns  {*} value stored in context
         */
        req.getAll = function getAll() {
            return data;
        };

        return next();
    };
}
This plugin creates `req.set(key, val)` and `req.get(key)` methods for
setting and retrieving request specific data.

@public
@function context
@returns {Function} Handler
@example
server.pre(restify.plugins.pre.context());
server.get('/', [
    function(req, res, next) {
        req.set(myMessage, 'hello world');
        return next();
    },
    function two(req, res, next) {
        res.send(req.get(myMessage)); // => sends 'hello world'
        return next();
    }
]);