plugins/redirects.php

<?php
/**
 * Plugin Name: jquery-wp-content Redirection extensions
 * Description: Adds custom XML-RPC methods to control redirection.
 */

add_filter( 'template_redirect', function() {
	if ( is_404() ) {
		$url = trailingslashit( $_SERVER[ 'REQUEST_URI' ] );
	} elseif ( is_front_page() ) {
		$url = "/";
	} else {
		// Don't influence any other pages
		return;
	}

	// Check for redirects stored in the database
	$transient = get_option( 'jquery_redirects' );

	if ( $transient && !empty( $transient[ $url ] ) ) {
		wp_redirect( $transient[ $url ], 301 );
	}
} );

add_filter( 'xmlrpc_methods', function( $methods ) {
	$methods[ 'jq.setRedirects' ] = 'jq_set_redirects';
	return $methods;
} );

function jq_set_redirects( $args ) {
	global $wp_xmlrpc_server;

	// Authenticate
	$username = $args[ 1 ];
	$password = $args[ 2 ];

	if ( ! $user = $wp_xmlrpc_server->login( $username, $password ) ) {
		return $wp_xmlrpc_server->error;
	}

	// Store redirects
	return update_option( 'jquery_redirects', json_decode( $args[ 3 ], true ) );
}