Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 31919)
+++ wp-includes/functions.php	(working copy)
@@ -4668,7 +4668,7 @@
 
 	if ( $same_domain ) {
 		?>
-		<div id="wp-auth-check-form" data-src="<?php echo esc_url( add_query_arg( array( 'interim-login' => 1 ), $login_url ) ); ?>"></div>
+		<div id="wp-auth-check-form" data-src="<?php echo esc_url( apply_filters( 'interim_login_url', add_query_arg( array( 'interim-login' => 1 ), $login_url ) ) ); ?>"></div>
 		<?php
 	}