wp-prometheus/src/Endpoint/MetricsEndpoint.php

<?php
/**
 * Metrics endpoint class.
 *
 * @package WP_Prometheus
 */

namespace Magdev\WpPrometheus\Endpoint;

use Magdev\WpPrometheus\Metrics\Collector;

// Prevent direct file access.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

/**
 * MetricsEndpoint class.
 *
 * Provides the /metrics endpoint for Prometheus scraping.
 */
class MetricsEndpoint {

    /**
     * Metrics collector instance.
     *
     * @var Collector
     */
    private Collector $collector;

    /**
     * Constructor.
     *
     * @param Collector $collector Metrics collector instance.
     */
    public function __construct( Collector $collector ) {
        $this->collector = $collector;
        $this->init_hooks();
    }

    /**
     * Initialize WordPress hooks.
     *
     * @return void
     */
    private function init_hooks(): void {
        add_action( 'init', array( $this, 'register_endpoint' ) );
        add_action( 'template_redirect', array( $this, 'handle_request' ) );
    }

    /**
     * Register the metrics endpoint rewrite rule.
     *
     * @return void
     */
    public function register_endpoint(): void {
        add_rewrite_rule(
            '^metrics/?$',
            'index.php?wp_prometheus_metrics=1',
            'top'
        );

        add_rewrite_tag( '%wp_prometheus_metrics%', '([^&]+)' );
    }

    /**
     * Handle the metrics endpoint request.
     *
     * @return void
     */
    public function handle_request(): void {
        if ( ! get_query_var( 'wp_prometheus_metrics' ) ) {
            return;
        }

        // Authenticate the request.
        if ( ! $this->authenticate() ) {
            status_header( 401 );
            header( 'WWW-Authenticate: Bearer realm="WP Prometheus Metrics"' );
            header( 'Content-Type: text/plain; charset=utf-8' );
            echo 'Unauthorized';
            exit;
        }

        // Output metrics.
        status_header( 200 );
        header( 'Content-Type: text/plain; version=0.0.4; charset=utf-8' );
        header( 'Cache-Control: no-cache, no-store, must-revalidate' );
        header( 'Pragma: no-cache' );
        header( 'Expires: 0' );

        // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Prometheus format.
        echo $this->collector->render();
        exit;
    }

    /**
     * Authenticate the metrics request.
     *
     * @return bool
     */
    private function authenticate(): bool {
        $auth_token = get_option( 'wp_prometheus_auth_token', '' );

        // If no token is set, deny access.
        if ( empty( $auth_token ) ) {
            return false;
        }

        // Check for Bearer token in Authorization header.
        $auth_header = $this->get_authorization_header();
        if ( ! empty( $auth_header ) && preg_match( '/Bearer\s+(.*)$/i', $auth_header, $matches ) ) {
            return hash_equals( $auth_token, $matches[1] );
        }

        // Check for token in query parameter (less secure but useful for testing).
        // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Auth token check.
        if ( isset( $_GET['token'] ) && hash_equals( $auth_token, sanitize_text_field( wp_unslash( $_GET['token'] ) ) ) ) {
            return true;
        }

        return false;
    }

    /**
     * Get the Authorization header from the request.
     *
     * @return string
     */
    private function get_authorization_header(): string {
        if ( isset( $_SERVER['HTTP_AUTHORIZATION'] ) ) {
            return sanitize_text_field( wp_unslash( $_SERVER['HTTP_AUTHORIZATION'] ) );
        }

        if ( isset( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) ) {
            return sanitize_text_field( wp_unslash( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) );
        }

        if ( function_exists( 'apache_request_headers' ) ) {
            $headers = apache_request_headers();
            if ( isset( $headers['Authorization'] ) ) {
                return sanitize_text_field( $headers['Authorization'] );
            }
        }

        return '';
    }
}