koa2构建api出现跨域，通过koa2cors设置无效

url: message/send

method: post

content-type:application/json

 app.use(cors({

        origin: '*',

        credentials: true,

        exposeHeaders: ['WWW-Authenticate', 'Server-Authorization'],

        allowMethods: ['OPTIONS', 'GET', 'PUT', 'POST', 'DELETE'],

        allowHeaders: ['x-requested-with', 'accept', 'origin', 'content-type'],

        maxAge: 1728000

   }))