code: function SAMLCredentials(params) {
      AWS.Credentials.call(this);
      this.expired = true;
      this.params = params;
      this.service = new AWS.STS({params: this.params});
    }
docs: Creates a new credentials object.
  @param (see AWS.STS.assumeRoleWithSAML)
  @example Creating a new credentials object
  AWS.config.credentials = new AWS.SAMLCredentials({
  RoleArn: 'arn:aws:iam::1234567890:role/SAMLRole',
  PrincipalArn: 'arn:aws:iam::1234567890:role/SAMLPrincipal',
  SAMLAssertion: 'base64-token', // base64-encoded token from IdP
  });
  @see AWS.STS.assumeRoleWithSAML