Using aws-sdk npm package with DefaultProviderChain

sts-example.js

const AWS = require('aws-sdk');

// Gets copy of default provider chain
const chain = AWS.CredentialProviderChain.defaultProviders.slice(0);

// Inserts additional check for specific profile in ~/.aws/credentials file
chain.splice(2, 0, () => new AWS.SharedIniFileCredentials({profile: 'readonly_user'}));

// Creates credential resolver that uses my custom provider chain
const credentialProvider = new AWS.CredentialProviderChain(chain);

// Create sts client for later requests
let sts = new AWS.STS({
    credentialProvider,
    credentials: null,  // This is necessary because of bug (https://github.com/aws/aws-sdk-js/pull/1367)
    region: 'us-east-1'
});

// Figure out which set of credentials I ended up using
sts.getCallerIdentity({}, (_, data) => {
  console.log(data);
});

// Kill off the sts client for the hell of it
sts = null;