var nano = require('nano')('http://localhost:5984')
const username = 'test'
const userpass = '123123'
const callback = console.log // this would normally be some callback
const cookies = {} // store cookies, normally redis or something

nano.auth(username, userpass, function (err, body, headers)
{
   if (err)
   {
    return callback(err);
   }

   if (headers && headers['set-cookie'])
   {
    cookies[username] = headers['set-cookie'];
    console.log(cookies)
   }

   if (!err)
   {
    callback("success ", "it worked");
   }
});

{ test:
   [ 'AuthSession=dGVzdDo1QTQ1RTFENDoVzjtA5v82S3bJRyI9Mz_J9dXrWA; Version=1;
   Expires=Thu, 28-Dec-2017 22:43:56 GMT; Max-Age=600; Path=/; HttpOnly' ] }
   success  it worked

name: 'Error',
  error: 'unauthorized',
  reason: 'Authentication required.',
  scope: 'couch',
  statusCode: 401,
  request:
   { method: 'POST',
     headers:
      { 'content-type': 'application/x-www-form-urlencoded; charset=utf-8',
        accept: 'application/json' },
     uri: 'http://localhost:5984/_session',
     body: 'name=test&password=123123' },
  headers:
   { 'www-authenticate': 'Basic realm="server"',
     date: 'Fri, 29 Dec 2017 06:42:10 GMT',
     'content-type': 'application/json',
     'cache-control': 'must-revalidate',
     statusCode: 401,
     uri: 'http://localhost:5984/_session' },
  errid: 'non_200',
  description: 'couch returned 401' }