Good — this is the clean, high-assurance way to do it.

You want:

> Laravel proves it sent the request
> WordPress verifies it
> WordPress cannot forge requests
> No shared secret exists

That’s **asymmetric signing**.

Laravel holds a **private key**.
WordPress holds the **public key**.

Only Laravel can create valid signatures.

---

# 🔐 High-Level Flow

1. Laravel builds request payload
2. Laravel signs payload with **private key**
3. Laravel sends:

   * Body
   * Timestamp
   * Signature header
4. WordPress:

   * Reconstructs signed message
   * Verifies signature using **public key**
   * Checks timestamp window
   * Accepts or rejects

No shared secret anywhere.

---

# Step 1 — Generate Key Pair (One Time)

On your Laravel server:

```bash
openssl genpkey -algorithm RSA -out laravel_private.pem -pkeyopt rsa_keygen_bits:4096
openssl rsa -pubout -in laravel_private.pem -out laravel_public.pem
```

You now have:

* `laravel_private.pem` → stays on Laravel server only
* `laravel_public.pem` → copy to WordPress

---

# Step 2 — Store Keys Securely

### Laravel

Store private key:

* In `.env`
* Or outside project root
* Never commit to git

Example `.env`:

```
WP_SIGNING_PRIVATE_KEY=/path/to/laravel_private.pem
```

---

### WordPress

Put public key in:

`wp-config.php`

```php
define('LARAVEL_PUBLIC_KEY', file_get_contents(__DIR__ . '/laravel_public.pem'));
```

Or paste contents directly.

Public key is safe to expose — it cannot sign.

---

# Step 3 — Laravel: Sign the Request

Example in Laravel:

```php
$privateKey = openssl_pkey_get_private(
    file_get_contents(env('WP_SIGNING_PRIVATE_KEY'))
);

$timestamp = time();
$body = json_encode($payload);

$message = $timestamp . '.' . $body;

openssl_sign(
    $message,
    $signature,
    $privateKey,
    OPENSSL_ALGO_SHA256
);

$signature = base64_encode($signature);

Http::withHeaders([
    'X-Timestamp' => $timestamp,
    'X-Signature' => $signature,
])->post($wpUrl, $payload);
```

---

# Step 4 — WordPress: Verify Signature

Inside your REST endpoint callback:

```php
$timestamp = $_SERVER['HTTP_X_TIMESTAMP'] ?? '';
$signature = $_SERVER['HTTP_X_SIGNATURE'] ?? '';

$body = file_get_contents('php://input');
$message = $timestamp . '.' . $body;

$publicKey = openssl_pkey_get_public(LARAVEL_PUBLIC_KEY);

$verified = openssl_verify(
    $message,
    base64_decode($signature),
    $publicKey,
    OPENSSL_ALGO_SHA256
);

if (!$verified) {
    return new WP_Error('invalid_signature', 'Signature invalid', ['status' => 403]);
}
```

---

# Step 5 — Add Replay Protection (Critical)

Add timestamp validation:

```php
if (abs(time() - (int)$timestamp) > 300) {
    return new WP_Error('expired', 'Request expired', ['status' => 403]);
}
```

This prevents replay attacks.

---

# 🔒 Why This Is Stronger Than HMAC

| Feature                             | HMAC   | Asymmetric |
| ----------------------------------- | ------ | ---------- |
| Shared secret                       | Yes    | No         |
| WP can forge                        | Yes    | No         |
| DB compromise exposes signing power | Yes    | No         |
| Clean trust boundary                | Medium | High       |

If WordPress DB is compromised:

* Attacker gets public key
* Cannot sign anything
* Cannot impersonate Laravel

That’s the big win.

---

# 🧠 Important Detail

Always sign:

```
timestamp + "." + raw_body
```

NOT parsed JSON.

JSON formatting differences will break verification.

---

# 🚨 Don’t Forget

* Enforce HTTPS
* Use constant-time comparison if manually comparing
* Reject missing headers
* Optionally add key version header for rotation later

---

# 🔄 Bonus: Key Rotation Strategy

You can:

* Add `X-Key-Id` header
* Store multiple public keys in WP
* Rotate Laravel private key
* Remove old public key later

Professional-grade setup.

---

# 🎯 Is This Overkill?

For:

* Financial operations
* Order sync
* Account provisioning
* Anything destructive

No — this is ideal.

For simple content sync?
HMAC is usually enough.

---

# Final Architecture

Laravel → signs with private key
WordPress → verifies with public key
Timestamp → prevents replay
HTTPS → prevents MITM

That’s cryptographically sound.

---

If you want, I can also show:

* How to wrap this in Laravel middleware
* How to wrap verification into WP REST permission callback
* Or how to structure the signed message more formally

You’re designing this the right way.