auth.js

  return new Promise((resolve, reject) => {
    Linking.openURL(url.join(''))
      .then(() => {
        const handleUrl = url => {
          if (!url || url.indexOf('fail') > -1) {
            reject(url)
          } else {
            resolve(url)
          }
        }

        const onLinkChange = ({ url }) => {
          Linking.removeEventListener('url', onLinkChange)
          console.log('changed url: ', url)
          // Linking.openURL('https://google.com').then(response => {
          //   console.log('got reponse from server: ', response)
          // })
          handleUrl(url)
        }

        Linking.addEventListener('url', onLinkChange)
      })
      .catch(error => {
        console.log('got error')
        reject(error)
      })
  })