secureFetch.js

import config from '../app.config.js';

export default async (uri, options) => {
  options = options || {};
  let token = JSON.parse(localStorage.getItem('token'));
  if (!token || (new Date()) - (new Date(token.expiresAt))  < 30) {
    await getAccessToken();
    token = JSON.parse(localStorage.getItem('token'));
  }

  // make the call with the access token
  if(token){
    const optionHeaders = Object.assign({}, options.headers, { 'Authorization': 'Bearer ' + token.access_token });
    const optsWithAuthHeader = Object.assign({}, options, { headers: optionHeaders });
    return fetch(uri, optsWithAuthHeader);
  }else{
    return fetch(uri, options);
  }
};

const getAccessToken = () => {
  let formData = new FormData();
  formData.append('grant_type', 'client_credentials');
  formData.append('scope', 'access_token');
  fetch(config.okta.tokenUrl, {
      method: 'POST',
      headers: {
        Authorization: 'Basic ' + btoa(config.okta.clientId+':'+config.okta.clientSecret),
        'Content-Type': 'application/x-www-form-urlencoded'
      },
      body: formData
    })
    .then(res => res.json())
    .then(token => {
      token.expiresAt = new Date() + token.expires_in;
      localStorage.setItem('token', JSON.stringify(token));
    })
    .catch(err => console.error(err));
};