I have found the solution though with a little overheads.
Steps are:
1> Create a PHP script in you own server (say named, YRedirect.php).
2> Pest the following code in it-
<?php
$query = $_SERVER['QUERY_STRING'];
header("Location: YOUR_APP_ID_OR_BUNDLE_ID://oauth-response?" . $query);
?>
3> Add an URL Scheme in your info.plist file with the YOUR_APP_ID_OR_BUNDLE_ID.
That's it and you are DONE with the authentication problem.
But, I am still on retrieving contact info from Yahoo!.
Thanks all.