Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 41804)
+++ wp-includes/pluggable.php	(working copy)
@@ -1213,6 +1213,20 @@
 	if ( !$is_IIS && PHP_SAPI != 'cgi-fcgi' )
 		status_header($status); // This causes problems on IIS and some FastCGI setups
 
+	/**
+	 * Filters the x-redirect-by header, allows applications to identify themselves when they're doing a redirect.
+	 *
+	 * @since 5.0
+	 *
+	 * @param string $x_redirect_by The application doing the redirect.
+	 * @param int    $status        Status code to use.
+	 * @param string $location      The path to redirect to.
+	 */
+	$x_redirect_by = apply_filters( 'x_redirect_by', 'WordPress', $status, $location );
+	if ( is_string( $x_redirect_by ) ) {
+		header( sprintf( "X-Redirect-By: %s", $x_redirect_by  ) );
+	}
+
 	header("Location: $location", true, $status);
 
 	return true;