I would like the ability to send data from php server1 to php server2

Integrity of the received data is of paramount importance, any modification must result in an error.
  To ensure the integrity of data being sent from one PHP server to another, you can use digital signatures. Digital signatures use cryptography to provide a tamper-evident seal on the data, ensuring that the data has not been modified during transmission.

Here are the steps you can follow to implement digital signatures in PHP:

1. Choose a digital signature library: There are several digital signature libraries available for PHP, such as OpenSSL, Crypt::SSL, and PHP-DS. Choose one that best fits your requirements.
2. Generate a private key: You will need a private key to sign the data. The private key should be kept secret and protected from unauthorized access.
3. Generate a digital signature: Use the private key to generate a digital signature of the data you want to send. The digital signature can be generated using the `openssl_sign()` function in OpenSSL, or using the `crypt_sign()` function in Crypt::SSL.
4. Send the signed data: Send the signed data to the recipient's server.
5. Verify the digital signature: On the recipient's server, use the public key to verify the digital signature. If the digital signature is valid, the data has not been modified during transmission.

Here is an example of how you can use OpenSSL to generate and verify a digital signature in PHP:
To ensure the integrity of the data sent from one PHP server to another, you can use a combination of cryptographic techniques. One of the most common ways to achieve this is by using a hash function along with a secret key to create a HMAC (Hash-based Message Authentication Code). This way, you can verify that the data has not been tampered with during transmission.

Here's a step-by-step guide on how to implement this:

### Step 1: Sending Data from Server1

1. **Prepare the data**: Serialize the data you want to send.
2. **Generate a HMAC**: Use a secret key to create a HMAC of the serialized data.
3. **Send the data and HMAC**: Send both the serialized data and the HMAC to Server2.

```php
// server1.php

// The data you want to send
$data = [
    'name' => 'John Doe',
    'email' => 'john@example.com',
];

// Serialize the data
$serializedData = json_encode($data);

// Your secret key (keep this safe and do not expose it)
$secretKey = 'your_secret_key';

// Generate HMAC
$hmac = hash_hmac('sha256', $serializedData, $secretKey);

// Prepare the payload
$payload = [
    'data' => $serializedData,
    'hmac' => $hmac,
];

// Send the data to Server2 (using cURL for example)
$