(Objective-C) 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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#import <CkoJsonObject.h>
#import <CkoStringBuilder.h>
#import <NSString.h>
#import <CkoHttp.h>
#import <CkoHttpResponse.h>
#import <CkoCert.h>
#import <CkoRsa.h>

// 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.

BOOL success;

// Provide information needed for Chilkat to automatically get an OAuth2 access token as needed.
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json UpdateString: @"client_id" value: @"APP_ID"];
[json UpdateString: @"client_secret" value: @"APP_PASSWORD"];
[json UpdateString: @"resource" value: @"https://vault.azure.net"];
[json UpdateString: @"token_endpoint" value: @"https://login.microsoftonline.com/TENANT_ID/oauth2/token"];

// In this example, we'll sign the SHA256 hash of the string "This is a test"
CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
NSString *signedString = @"This is a test";
[sb Append: signedString];
NSString *hash_base64url = [sb GetHash: @"sha256" encoding: @"base64url" charset: @"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..

CkoJsonObject *jsonBody = [[CkoJsonObject alloc] init];
[jsonBody UpdateString: @"alg" value: @"RS256"];
[jsonBody UpdateString: @"value" value: hash_base64url];

CkoHttp *http = [[CkoHttp alloc] init];

// 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.AuthToken = [json Emit];

[http SetUrlVar: @"certName" value: @"importCert01"];
[http SetUrlVar: @"certVersion" value: @"7140c8755ed14839b5d86a9f7e7f0497"];
// Note: Replace "VAULT_NAME" with the name of your Azure key vault.
NSString *url = @"https://VAULT_NAME.vault.azure.net/keys/{$certName}/{$certVersion}/sign?api-version=7.4";
CkoHttpResponse *resp = [http PostJson3: url contentType: @"application/json" json: jsonBody];
if (http.LastMethodSuccess == NO) {
    // This means something failed before we got a response.
    NSLog(@"%@",http.LastErrorText);
    return;
}

int statusCode = [resp.StatusCode intValue];

CkoJsonObject *jsonResp = [[CkoJsonObject alloc] init];
[resp GetBodyJson: jsonResp];

jsonResp.EmitCompact = NO;
NSLog(@"%@",[jsonResp Emit]);

if (statusCode != 200) {
    NSLog(@"%@",@"Failed.");
    return;
}

// 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.
// 
CkoCert *cert = [[CkoCert alloc] init];
success = [cert LoadFromFile: @"qa_data/certs/chilkat_code_signing_2024.cer"];
if (success == NO) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

CkoRsa *rsa = [[CkoRsa alloc] init];
// Tell the RSA object to use the cert's public key.
success = [rsa SetX509Cert: cert usePrivateKey: NO];
if (success == NO) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Verify the signature using the cert's public key against the original string.
rsa.EncodingMode = @"base64url";
BOOL valid = [rsa VerifyStringENC: signedString hashAlg: @"sha-256" sig: [jsonResp StringOf: @"value"]];
NSLog(@"%@%d",@"signature valid = ",valid);