Site Bridge

WordPress plugin that exposes a secure, HMAC-signed REST API for programmatic site management. Built for autonomous AI agents and CI/CD pipelines.

Site Bridge lets a remote client safely:

• Read and modify pages/posts (including builder content — Breakdance, Elementor, Gutenberg blocks)
• Install / activate / deactivate plugins from a ZIP
• Read and write files inside whitelisted directories
• Purge caches across 13+ caching plugins (WP Rocket, LiteSpeed, W3TC, WP Super Cache, …)
• Read form submissions
• Inspect audit log and error log

All endpoints are protected by HMAC-SHA256 signatures, optional IP whitelist, rate-limit, and a kill-switch. The plugin does not use WordPress Application Passwords — its custom header (X-SB-Signature) flies under the radar of typical WAFs (NinjaFirewall, Wordfence, Imunify360) that aggressively gate password-based login attempts.

Status: v1.0.3 — production-ready. Used in a 7-site network in real-world day-to-day operations. AI agents (Claude Code, GPT, etc.) interact through it via the reference Python client.

Why this exists

WordPress's built-in REST API can be managed via Application Passwords + HTTP Basic Auth, but in practice that path is often broken by:

• WAF plugins treating every API call as a login attempt and rate-limiting it
• wp_unslash silently corrupting large JSON-in-meta payloads (Breakdance _breakdance_data, Elementor _elementor_data — see #fix-history below)
• Apache stripping Authorization headers on shared hosting
• WPS Hide Login breaking the login-style auth flow

Site Bridge sidesteps all of these:

• Custom header X-SB-Signature — WAFs don't recognise it as a login attempt
• Direct SQL writes for wp_posts.post_content and wp_postmeta.meta_value — bypass wp_unslash and sanitize_meta filters that mangle large payloads
• Per-request HMAC — secret never travels over the wire; replay window 5 minutes
• Self-contained auth — doesn't piggyback on WP's login subsystem at all

Endpoints (v1.0.3)

REST namespace: /wp-json/sb/v1/

Builder compatibility

Site Bridge does not depend on any specific page builder. Builder-specific cache invalidation kicks in only when the relevant meta keys are touched:

You can have multiple builders on the same site — Site Bridge handles each independently.

Security model

Auth

Every request to /wp-json/sb/v1/* must include two headers:

X-SB-Timestamp: <unix-seconds>
X-SB-Signature: <hex>

The signature is computed as:

message    = TIMESTAMP + "\n" + METHOD + "\n" + PATH + "\n" + sha256_hex(BODY)
signature  = HMAC-SHA256(secret, message)   // hex, lowercase

Where:

• TIMESTAMP — the same value you sent in X-SB-Timestamp
• METHOD — uppercase HTTP method
• PATH — REST route without the /wp-json prefix, e.g. /sb/v1/pages/123
• BODY — raw request body bytes; empty string for GET
• sha256_hex(BODY) — hex-encoded SHA-256 of the body bytes

Defense in depth

1. HMAC on every endpoint (including /ping)
2. Timestamp tolerance ±5 min (replay protection)
3. IP whitelist (optional, IPv4 CIDR supported)
4. Rate limit: 5 failed auth attempts in 5 min → IP banned for 1 hour, email alert
5. Audit log — every request (success and failure) recorded in wp_sb_audit
6. Email alerts on auth-failure bursts and dangerous operations (plugin install, file write, backup restore)
7. Kill switch — define('SITE_BRIDGE_DISABLED', true); in wp-config instantly disables all endpoints (returns 503)
8. File whitelist — /files endpoints are restricted to wp-content/plugins/* (except site-bridge's own dir), wp-content/themes/*, wp-content/uploads/*, wp-content/mu-plugins/*. wp-config.php, .htaccess, wp-admin/, wp-includes/ are explicitly denied
9. hash_equals — timing-safe signature comparison
10. Graceful secret rotation — supports a SITE_BRIDGE_SECRET_PREVIOUS constant for a grace period during rotation

Installation

1. Generate a secret

python3 -c "import secrets; print(secrets.token_urlsafe(48))"
# example: k7m9x4q...64chars...VkR3

2. Add constants to wp-config.php

Place these before /* That's all, stop editing! */:

// REQUIRED
define( 'SITE_BRIDGE_SECRET', '<your generated secret>' );

// RECOMMENDED — restrict by client IP
define( 'SITE_BRIDGE_ALLOWED_IPS', '203.0.113.42' );      // CSV, IPv4 CIDR supported

// OPTIONAL
define( 'SITE_BRIDGE_SECRET_PREVIOUS', '' );              // for zero-downtime rotation
define( 'SITE_BRIDGE_TIMESTAMP_TOLERANCE', 300 );          // seconds
define( 'SITE_BRIDGE_ALERT_EMAIL', '' );                  // empty = admin_email
define( 'SITE_BRIDGE_LOG_LEVEL', 'info' );                // info | debug — use debug during initial setup, then switch to info
define( 'SITE_BRIDGE_DISABLED', false );                  // kill switch

3. Install the plugin

Either:

• Copy the site-bridge/ folder to wp-content/plugins/ via FTP/SSH, then activate via wp-admin
• Or upload site-bridge.zip via wp-admin → Plugins → Add New → Upload

On activation, two tables are created:

• {prefix}sb_audit — request log
• {prefix}sb_page_backups — page snapshots (auto + manual)

Quick start (Python)

from sb_client import SiteBridge

sb = SiteBridge("my-site")           # name from ~/.sb-sites.json

print(sb.ping())                     # {"status": "ok", ...}

# Read a page (incl. all meta — for builder content)
page = sb.get_page(123)

# Update content (works for Gutenberg)
sb.update_page(123, content="<!-- wp:paragraph --><p>Hi</p><!-- /wp:paragraph -->")

# Update builder meta (Breakdance / Elementor)
sb.update_page(123, meta={"_breakdance_data": new_json})

# Gutenberg block-level edit
blocks = sb.get_blocks(123)["blocks"]
blocks[0]["attrs"]["align"] = "center"
sb.put_blocks(123, blocks)

# Purge caches (auto-detects what's installed)
sb.purge_cache()

# Deploy a plugin ZIP
sb.upload_plugin("/path/to/my-plugin.zip", activate=True, overwrite=True)

Config file

Default location: ~/.sb-sites.json (override via SB_SITES_CONFIG env var):

{
  "sites": {
    "my-site": {
      "url": "https://example.com",
      "site_bridge_secret": "<same value as SITE_BRIDGE_SECRET in wp-config.php>"
    }
  }
}

Quick start (curl)

SECRET='your-secret-here'
TS=$(date +%s)
METHOD='GET'
PATH='/sb/v1/ping'
BODY=''
BODY_SHA=$(echo -n "$BODY" | sha256sum | awk '{print $1}')
MSG=$(printf '%s\n%s\n%s\n%s' "$TS" "$METHOD" "$PATH" "$BODY_SHA")
SIG=$(echo -n "$MSG" | openssl dgst -sha256 -hmac "$SECRET" | awk '{print $2}')

curl -H "X-SB-Timestamp: $TS" -H "X-SB-Signature: $SIG" \
     "https://example.com/wp-json/sb/v1/ping"

Reference clients

• Python — sb_client.py (included in repo)
• JavaScript / Node.js — see examples/sb_client.js — minimal HMAC client using node:crypto
• AI agents — see AGENTS.md — full LLM-friendly protocol & recipe doc

Configuration reference

All configuration lives in wp-config.php. No admin-UI settings — keeping it that way prevents a compromised wp-admin from disabling auth.

Secret rotation

If you suspect the secret is compromised (or just doing routine rotation):

1. Generate a new secret.
2. Move old secret to SITE_BRIDGE_SECRET_PREVIOUS, put new one in SITE_BRIDGE_SECRET.
3. Update your client config to use the new secret.
4. After 24h (or once all clients are confirmed updated), remove SITE_BRIDGE_SECRET_PREVIOUS.

During the grace period, requests signed with either secret are accepted.

Audit log

Every request to /wp-json/sb/v1/* writes a row to {prefix}sb_audit:

Auto-cleanup: rows older than 90 days are removed via daily cron.

Read via API: GET /audit-log?limit=100&since=2026-01-01&auth_status=ok

File operations

/files endpoints are restricted to a whitelist of directory prefixes:

• ✅ wp-content/plugins/* (except site-bridge's own folder — use /plugins/upload for self-update)
• ✅ wp-content/themes/*
• ✅ wp-content/uploads/*
• ✅ wp-content/mu-plugins/*

Explicitly denied:

• ❌ wp-admin/*, wp-includes/*
• ❌ wp-config.php, .htaccess, .htpasswd, .env, dotfiles at root

Each write is preceded by an automatic backup to wp-content/uploads/site-bridge-backups/.

Size limit: 20 MB per file.

What is not protected by the API

Out of scope (use FTP/SSH/wp-admin):

• wp-config.php editing — too dangerous; secret lives here anyway
• .htaccess modification
• Direct DB queries (only meta/post writes through dedicated endpoints)
• WordPress core file modification

This is intentional — the smaller the API surface, the smaller the blast radius if the secret leaks.

Fix history

1.0.2 — Gutenberg + Elementor + 13 cache plugins

• Gutenberg block-level API: GET/PUT /pages/{id}/blocks using native parse_blocks() / serialize_blocks()
• Fix: wp_unslash on post_content. wp_update_post() strips one slash layer, corrupting Gutenberg block attributes (`) and any post content with backslashes. Replaced withSB_Post::set_fields_raw()— direct SQLUPDATE wp_posts` bypassing WP-layer.
• Fix: auto-backup on any write, not only meta updates (was a bug — content-only PATCH skipped backup).
• Generalised builder cache invalidation: one function now handles Breakdance, Elementor, WPBakery — and any future builder added.
• Restore_backup also writes through SB_Post::set_fields_raw() for byte-perfect restoration.
• 13 cache-plugin support: WP Rocket, LiteSpeed, W3 Total Cache, WP Super Cache, Cache Enabler, WP Fastest Cache, Hummingbird, SG Optimizer, Swift Performance, Comet Cache, Autoptimize, Seraphinite, WP Object Cache.

1.0.1 — wp_unslash fix for meta

• Critical: update_post_meta() / add_post_meta() apply wp_unslash() to the stored value, stripping one layer of backslash escapes. For large JSON-in-meta blobs (Breakdance _breakdance_data ≈ 500 KB, Elementor _elementor_data), this silently corrupts the stored bytes (≈ 70 KB lost per typical Breakdance page). Replaced with SB_Meta::set() — direct SQL INSERT/UPDATE wp_postmeta bypassing WP-layer.
• Auto-invalidation of Breakdance CSS caches after _breakdance_data writes (meta + physical files in wp-content/uploads/breakdance/css/).

1.0.0

• First public release. Pages, backups, plugins, files, cache, forms, audit-log, error-log endpoints. HMAC-SHA256 auth.

Contributing

Issues and pull requests welcome at https://github.com/canabeo/site-bridge.

For security issues, please email instead of opening a public issue. See SECURITY.md.

License

GPL v2 or later. See LICENSE.