<?php
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use Psr\Http\Message\ResponseInterface;

/**
 * @var ResponseInterface $response
 *
 * Let's assume we have a valid ResponseInterface object already.
 * (Most likely, after doing normal framework things.)  
 */

$sapient = new Sapient();
$serverSignSecret = new SigningSecretKey(
    Base64UrlSafe::decode(
        'q6KSHArUnD0sEa-KWpBCYLka805gdA6lVG2mbeM9kq82_Cwg1n7XLQXXXHF538URRov8xV7CF2AX20xh_moQTA=='
    )
);

$signedResponse = $sapient->signResponse($response, $serverSignSecret);

<?php
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\Exception\{
    HeaderMissingException,
    InvalidMessageException
};
use Psr\Http\Message\ResponseInterface;

/**
 * @var ResponseInterface $response
 *
 * Let's assume we have a valid ResponseInterface object already.
 * (Most likely the result of an HTTP request to the server.)  
 */

$sapient = new Sapient();
$serverPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'NvwsINZ-1y0F11xxed_FEUaL_MVewhdgF9tMYf5qEEw='
    )
);

try {
    $verified = $sapient->verifySignedResponse($response, $serverPublicKey);
} catch (HeaderMissingException $ex) {
    /* The server didn't provide a header. Discard and log the error! */
} catch (InvalidMessageException $ex) {
    /* Invalid signature for the message. Discard and log the error! */
}

<?php
use GuzzleHttp\Client;
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Adapter\Guzzle as GuzzleAdapter;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use ParagonIE\Sapient\Exception\InvalidMessageException;

$http = new Client([
    'base_uri' => 'https://your-api.example.com'
]);
$sapient = new Sapient(new GuzzleAdapter($http));

// Keys
$clientSigningKey = new SigningSecretKey(
    Base64UrlSafe::decode(
        'AHxoibWhTylBMgFzJp6GGgYto24PVbQ-ognw9SPnvKppfti72R8By8XnIMTJ8HbDTks7jK5GmAnvtzaj3rbcTA=='
    )
);
$serverPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'NvwsINZ-1y0F11xxed_FEUaL_MVewhdgF9tMYf5qEEw='
    )
);

// We use an array to define our message
$myMessage = [
    'date' => (new DateTime)->format(DateTime::ATOM),
    'body' => [
        'test' => 'hello world!'        
    ]
];

// Create the signed request:
$request = $sapient->createSignedJsonRequest(
    'POST',
     '/my/api/endpoint',
     $myMessage,
     $clientSigningKey
);

$response = $http->send($request);
try {
    /** @var array $verifiedResponse */
    $verifiedResponse = $sapient->decodeSignedJsonResponse(
        $response,
        $serverPublicKey
    );
} catch (InvalidMessageException $ex) {
    \http_response_code(500);
    exit;
}

 <?php
use GuzzleHttp\Client;
use GuzzleHttp\Psr7\ServerRequest;
use ParagonIE\ConstantTime\Base64UrlSafe;
use ParagonIE\Sapient\Adapter\Guzzle as GuzzleAdapter;
use ParagonIE\Sapient\Sapient;
use ParagonIE\Sapient\CryptographyKeys\SigningPublicKey;
use ParagonIE\Sapient\CryptographyKeys\SigningSecretKey;
use ParagonIE\Sapient\Exception\InvalidMessageException;

$http = new Client([
    'base_uri' => 'https://your-api.example.com'
]);
$sapient = new Sapient(new GuzzleAdapter($http));
 
$clientPublicKey = new SigningPublicKey(
    Base64UrlSafe::decode(
        'aX7Yu9kfAcvF5yDEyfB2w05LO4yuRpgJ77c2o9623Ew='
    )
);
$request = ServerRequest::fromGlobals();
try {
    /** @var array $decodedRequest */
    $decodedRequest = $sapient->decodeSignedJsonRequest(
        $request,
        $clientPublicKey
    );
} catch (InvalidMessageException $ex) {
    \http_response_code(500);
    exit;
}

/* Business logic goes here */

// Signing a response:
$serverSignSecret = new SigningSecretKey(
    Base64UrlSafe::decode(
        'q6KSHArUnD0sEa-KWpBCYLka805gdA6lVG2mbeM9kq82_Cwg1n7XLQXXXHF538URRov8xV7CF2AX20xh_moQTA=='
    )
);

$responseMessage = [
    'date' => (new DateTime)->format(DateTime::ATOM),
    'body' => [
        'status' => 'OK',
        'message' => 'We got your message loud and clear.'
    ]
];

$response = $sapient->createSignedJsonResponse(
    200,
    $responseMessage,
    $serverSignSecret
);
/* If your framework speaks PSR-7, just return the response object and let it
   take care of the rest. */