code: function WebIdentityCredentials(params) {
      AWS.Credentials.call(this);
      this.expired = true;
      this.params = params;
      this.params.RoleSessionName = this.params.RoleSessionName || 'web-identity';
      this.service = new AWS.STS({params: this.params});
      this.data = null;
    }
docs: Creates a new credentials object.
  @param (see AWS.STS.assumeRoleWithWebIdentity)
  @example Creating a new credentials object
  AWS.config.credentials = new AWS.WebIdentityCredentials({
  RoleArn: 'arn:aws:iam::1234567890:role/WebIdentity',
  WebIdentityToken: 'ABCDEFGHIJKLMNOP', // token from identity service
  RoleSessionName: 'web' // optional name, defaults to web-identity
  });
  @see AWS.STS.assumeRoleWithWebIdentity