如何在PHP SDK中使用JWT获取Docusign API访问令牌？

composer require firebase/php-jwt

use Firebase\JWT\JWT;

function generateJwtToken($expirationTime, $otherParams) {
    $privateKey = 'your_private_key';
    $issuer = 'your_issuer';
    $clientId = 'your_client_id';

    $payload = [
        'iss' => $issuer,
        'sub' => $clientId,
        'aud' => 'account-d.docusign.com',
        'exp' => $expirationTime,
        'iat' => time()
    ];

    return JWT::encode($payload, $privateKey, 'RS256');
}

function getAccessToken($jwtToken, $otherParams) {
    $url = 'https://account-d.docusign.com/oauth/token';
    $clientId = 'your_client_id';
    $clientSecret = 'your_client_secret';

    $postData = [
        'grant_type' => 'urn:ietf:params:oauth:grant-type:jwt-bearer',
        'assertion' => $jwtToken,
        'client_id' => $clientId,
        'client_secret' => $clientSecret
    ];

    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($postData));

    $response = curl_exec($ch);
    $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

    curl_close($ch);

    if ($httpCode === 200) {
        $responseData = json_decode($response, true);
        return $responseData['access_token'];
    } else {
        return false;
    }
}