Custom REST API Endpoint with Authentication

/**
 * Register a custom REST API endpoint.
 */
add_action( 'rest_api_init', function() {
    register_rest_route( 'mytheme/v1', '/projects', array(
        'methods'             => WP_REST_Server::READABLE,
        'callback'            => 'mytheme_get_projects',
        'permission_callback' => function() {
            return current_user_can( 'edit_posts' );
        },
        'args' => array(
            'per_page' => array(
                'default'           => 10,
                'sanitize_callback' => 'absint',
                'validate_callback' => function( $value ) {
                    return is_numeric( $value ) && $value > 0 && $value get_param( 'per_page' );

    $query = new WP_Query( array(
        'post_type'      => 'portfolio',
        'posts_per_page' => $per_page,
        'no_found_rows'  => true,
    ) );

    $projects = array_map( function( $post ) {
        return array(
            'id'      => $post->ID,
            'title'   => $post->post_title,
            'excerpt' => get_the_excerpt( $post ),
            'url'     => get_permalink( $post ),
        );
    }, $query->posts );

    return new WP_REST_Response( $projects, 200 );
}