npm install koa2-cors --save

const cors = require('koa2-cors');

...

// 允许跨域访问

app.use(cors({

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

  maxAge: 100,

  credentials: true,

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

  allowHeaders: ['Content-Type', 'Authorization', 'Accept', 'X-Custom-Header', 'anonymous'],

}));