code: function demuxSsa (params, cb) {
    assert.equal(typeof params, 'object')
    assert.equal(typeof params._ssa, 'object')
    assert.equal(typeof cb, 'function')
    const req = params._ssa.req
    const res = params._ssa.res
    const nw = xtend(params)
    delete nw._ssa
    cb(req, res, nw)
  }
docs: demux an object into server params and pass them into a function (obj, fn) -> null