Post form data with axios in Node.js

You might be able to use Content-Type: 'application/x-www-form-urlencoded'. I ran into a similar issue with https://login.microsoftonline.com where it was unable to handle incoming application/json.

var axios = require("axios");

axios({
  url: 'https://login.uber.com/oauth/v2/token',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
  data: `client_id=${encodeURIComponent('**')}&client_secret=${encodeURIComponent('**')}&grant_type=authorization_code&redirect_uri=${encodeURIComponent('http://localhost:8080/')}&code=${encodeURIComponent('**')}`
})
.then(function(response) {
  console.log(response.data)
})
.catch(function(error) {
  console.log(error)
})

You could also use a function to handle the translation to formUrlEncoded like so

const formUrlEncoded = x =>
   Object.keys(x).reduce((p, c) => p + `&${c}=${encodeURIComponent(x[c])}`, '')

var axios = require("axios");

axios({
  url: 'https://login.uber.com/oauth/v2/token',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
  data: formUrlEncoded({
     client_id: '***',
     client_secret: '***',
     grant_type: 'authorization_code',
     redirect_uri: 'http://localhost:8080/',
     code: '***' 
  })
})
.then(function(response) {
  console.log(response.data)
})
.catch(function(error) {
  console.log(error)
})