(PHP Extension) Azure Key Vault Sign with a Certificate's Private Key

See more Azure Key Vault Examples

Signs a hash using the private key of a certificate previously imported to an Azure Key Vault.

Note: This example requires Chilkat v9.5.0.96 or later.

For more information, see https://learn.microsoft.com/en-us/rest/api/keyvault/certificates/import-certificate/import-certificate?tabs=HTTP

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<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// See Azure Key Vault Get Certificates for a more detailed explanation
// for how Chilkat is automatically getting the OAuth2 access token for your application.

// Provide information needed for Chilkat to automatically get an OAuth2 access token as needed.
$json = new CkJsonObject();
$json->UpdateString('client_id','APP_ID');
$json->UpdateString('client_secret','APP_PASSWORD');
$json->UpdateString('resource','https://vault.azure.net');
$json->UpdateString('token_endpoint','https://login.microsoftonline.com/TENANT_ID/oauth2/token');

// In this example, we'll sign the SHA256 hash of the string "This is a test"
$sb = new CkStringBuilder();
$signedString = 'This is a test';
$sb->Append($signedString);
$hash_base64url = $sb->getHash('sha256','base64url','utf-8');

// We're going to send a POST to the following URL:
// POST {vaultBaseUrl}/keys/{key-or-cert-name}/{key-or-cert-version}/sign?api-version=7.4

// For example:

// POST https://VAULT_NAME.vault.azure.net/keys/CERT_NAME/CERT_VERSION/sign?api-version=7.4
// 
// {
//   "alg": "RS512",
//   "value": "RUE3Nzg4NTQ4QjQ5RjFFN0U2NzAyQzhDNEMwMkJDOTA1MTYyOTUzNjI5NDhBNzZDQTlFOTM1NDA2M0ZGMjk2Mg"
// }

// The alg can be one of the following
// ES256  ECDSA using P-256 and SHA-256
// ES256K ECDSA using P-256K and SHA-256
// ES384  ECDSA using P-384 and SHA-384
// ES512  ECDSA using P-521 and SHA-512
// PS256  RSASSA-PSS using SHA-256 and MGF1 with SHA-256
// PS384  RSASSA-PSS using SHA-384 and MGF1 with SHA-384
// PS512  RSASSA-PSS using SHA-512 and MGF1 with SHA-512
// RS256  RSASSA-PKCS1-v1_5 using SHA-256
// RS384  RSASSA-PKCS1-v1_5 using SHA-384
// RS512  RSASSA-PKCS1-v1_5 using SHA-512

// The sample POST above uses SHA512.  We'll instead sign a SHA256 hash..

$jsonBody = new CkJsonObject();
$jsonBody->UpdateString('alg','RS256');
$jsonBody->UpdateString('value',$hash_base64url);

$http = new CkHttp();

// Instead of providing an actual access token, we give Chilkat the information that allows it to 
// automatically fetch the access token using the OAuth2 client credentials flow.
$http->put_AuthToken($json->emit());

$http->SetUrlVar('certName','importCert01');
$http->SetUrlVar('certVersion','7140c8755ed14839b5d86a9f7e7f0497');
// Note: Replace "VAULT_NAME" with the name of your Azure key vault.
$url = 'https://VAULT_NAME.vault.azure.net/keys/{$certName}/{$certVersion}/sign?api-version=7.4';
// resp is a CkHttpResponse
$resp = $http->PostJson3($url,'application/json',$jsonBody);
if ($http->get_LastMethodSuccess() == false) {
    // This means something failed before we got a response.
    print $http->lastErrorText() . "\n";
    exit;
}

$statusCode = $resp->get_StatusCode();

$jsonResp = new CkJsonObject();
$resp->GetBodyJson($jsonResp);

$jsonResp->put_EmitCompact(false);
print $jsonResp->emit() . "\n";

if ($statusCode != 200) {
    print 'Failed.' . "\n";
    exit;
}

// A successful response body contains JSON like this:
// Note: Azure's documentation is not very clear, but base64url is the encoding, not "base64".
// {
//   "kid": "https://kvchilkat.vault.azure.net/keys/importCert01/7140c8755ed14839b5d86a9f7e7f0497",
//   "value": "JzWd2YF21gjtW ... Em37hKOQ"
// }

// Let's validate the signature using the cert's public key.
// This example will load the corresponding certificate from a local file and will verify the signature against the original data.
// 
$cert = new CkCert();
$success = $cert->LoadFromFile('qa_data/certs/chilkat_code_signing_2024.cer');
if ($success == false) {
    print $cert->lastErrorText() . "\n";
    exit;
}

$rsa = new CkRsa();
// Tell the RSA object to use the cert's public key.
$success = $rsa->SetX509Cert($cert,false);
if ($success == false) {
    print $rsa->lastErrorText() . "\n";
    exit;
}

// Verify the signature using the cert's public key against the original string.
$rsa->put_EncodingMode('base64url');
$valid = $rsa->VerifyStringENC($signedString,'sha-256',$jsonResp->stringOf('value'));
print 'signature valid = ' . $valid . "\n";

?>