WP-SSL-redirect.php

<?php

add_action( 'template_redirect', 'nlp_ssl_template_redirect', 1 );

function nlp_ssl_template_redirect() {
	if ( !is_ssl() && ! is_admin() ) {
		if ( 0 === strpos( $_SERVER['REQUEST_URI'], 'http:' ) ) {
			wp_redirect( preg_replace( '|^http://|', 'https://', $_SERVER['REQUEST_URI'] ), 301 );
			exit();
		} else {
			wp_redirect( 'https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'], 301 );
			exit();
		}
	}

	if (is_ssl()) {
		header("Strict-Transport-Security: max-age=31536000;");
	}
}