Generate base64 bearer token header in Node.js

index.js

const axios = require('axios')
// Testing on Twitter API.
// consumerKey and consumerSecret is a pair of keys associated with an app registered with Twitter API
const consumerKey = process.env.CONSUMER_KEY
const consumerSecret = process.env.CONSUMER_SECRET
const str = `${consumerKey}:${consumerSecret}`
// Base64 encode the request token and turn it into a value of the Authorization header
const authHeader = `Basic ${Buffer.from(str).toString('base64'}`
// Create an isntance of Axios
const instance = axios.create({
  baseURL: 'https://api.twitter.com'
})
async function getBearToken (authHeader) {
  instance.interceptors.request.use(config => {
    config.headers = authHeader
    // This param is required by the Twitter OAuth2
    config.params = { grant_type: 'client_credentials'}
    return config
  })
  try {
    const response = await instance.post('/oauth2/token')
    // Expect to see something like
    // {token_type: 'bearer', access_token: 'XXXXXXXXXXXXXXXXXXXXXXX'}
    console.log(response.data)
  }
  catch (error) {
    console.log(error)
  }
}