code: function makeMultipartParser(spec) {
    const opts = spec.validate.multipartOptions || {};
    if (typeof opts.autoFields === 'undefined') {
      opts.autoFields = true;
    }
    return async function parseMultipart(ctx, next) {
      if (!ctx.request.is('multipart/*')) {
        return ctx.throw(400, 'expected multipart');
      }
      ctx.request.parts = busboy(ctx, opts);
      await next();
    };
  }
docs: Creates stream/multipart-form body parser middleware.
  
  @param {Object} spec
  @return {async function}
  @api private