Unauthorized while embedding page in iframe

I am creating a application in Javascript and having one problem while embedding a page in iframe and getting unauthorized error.

<form method="POST" action="https//xxxx" id="myForm"  target="test"> 

    <input type="text" value="" name="SAMLResponse">
    <button type="submit">Submit</button>
</form>
<iframe name="test" id="test" style="height: 90vh; width: 100%;"></iframe>

It works without Iframe, if directly submit the page without using iframe page successfully open in same tab, but when using with iframe it gives unauthorized error 401