A standard practice of the component creation is to include a verifyCredentials.js which would initiate the actual verification process.

verifyCredentials.js file/programme is the one which initiates the first authorization process with an external resource that you integration flow is trying to connect.

Here is an example from the Microsoft Outlook component by elastic.io:

const MicrosoftGraph = require("msgraph-sdk-javascript");
const co = require('co');

// This function will be called by the platform to verify credentials
module.exports = function verifyCredentials(credentials, cb) {
  console.log('Credentials passed for verification %j', credentials);
  // Configuring MS Graph access library
  var client = MicrosoftGraph.init({
    defaultVersion: 'v1.0',
    debugLogging: true,
    authProvider: (done) => {
      done(null, credentials.oauth.access_token);
    }
  });
  // Doing verification
  var process = co(function*() {
    console.log('Fetching user information');
    var user = yield client.api('/me').get();
    console.log('Found user', user);
  });
  process.then(function () {
    console.log('Verification completed');
    cb(null, {verified: true});
  }).catch(err => {
    console.log('Error occured', err.stack || err);
    cb(null , {verified: false});
  });
};

In this example, we can see how the system uses data provided in the credentials part of the component.json to make the call to the external API provider (Service provider) for an access_token. If everything goes as planned elastic.io (Application) gets the necessary data back from the Service and stores it in the database.

We would like to highlight how the access_token is referenced here: credentials.oauth.access_token which shows that it is within the oauth structure of the credentials field. The whole oauth field is being saved in the database in the following form:

{
     "oauth":  {
       "access_token":"2YotnFZFEjr1zCsicMWpAA",
       "expires_in":3599,
       "ext_expires_in" : "0",
       "id_token" : "iuyaoixboiayudq807bd209db02ud92jd92",
       "refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
       "scope" : "calendars.read calendars.readwrite contacts.read mail.read mail.send user.read",
       "token_type":"bearer"
     }
}

Please note that this component is using an OAuth2 authorization method. For obvious reasons, we do not include the actual tokens here. And, the actual tokens are highly encrypted. In fact, this whole structure presented above is saved in an encrypted form within the credentials structure of our database.