code: function CognitoIdentityCredentials(params) {
      AWS.Credentials.call(this);
      this.expired = true;
      this.webIdentityCredentials = new AWS.WebIdentityCredentials(params);
      this.cognito = new AWS.CognitoIdentity({params: params});
      this.sts = new AWS.STS();
      this.params = params;
      this.data = null;
      this.identityId = null;
      this.loadCachedId();
    }
docs: Creates a new credentials object.
  @param (see AWS.STS.assumeRoleWithWebIdentity)
  @param (see AWS.CognitoIdentity.getOpenIdToken)
  @example Creating a new credentials object
  AWS.config.credentials = new AWS.CognitoIdentityCredentials({
  AccountId: '1234567890',
  IdentityPoolId: 'us-east-1:1699ebc0-7900-4099-b910-2df94f52a030',
  RoleArn: 'arn:aws:iam::1234567890:role/MYAPP-CognitoIdentity',
  Logins: { // optional tokens, used for authenticated login
  'graph.facebook.com': 'FBTOKEN',
  'www.amazon.com': 'AMAZONTOKEN',
  'accounts.google.com': 'GOOGLETOKEN'
  },
  RoleSessionName: 'web' // optional name, defaults to web-identity
  });
  @see AWS.STS.assumeRoleWithWebIdentity