(C#) Azure Key Vault Sign with a Certificate's Private Key

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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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// 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.
Chilkat.JsonObject json = new Chilkat.JsonObject();
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"
Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
string signedString = "This is a test";
sb.Append(signedString);
string 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..

Chilkat.JsonObject jsonBody = new Chilkat.JsonObject();
jsonBody.UpdateString("alg","RS256");
jsonBody.UpdateString("value",hash_base64url);

Chilkat.Http http = new Chilkat.Http();

// 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","importCert01");
http.SetUrlVar("certVersion","7140c8755ed14839b5d86a9f7e7f0497");
// Note: Replace "VAULT_NAME" with the name of your Azure key vault.
string url = "https://VAULT_NAME.vault.azure.net/keys/{$certName}/{$certVersion}/sign?api-version=7.4";
Chilkat.HttpResponse resp = http.PostJson3(url,"application/json",jsonBody);
if (http.LastMethodSuccess == false) {
    // This means something failed before we got a response.
    Debug.WriteLine(http.LastErrorText);
    return;
}

int statusCode = resp.StatusCode;

Chilkat.JsonObject jsonResp = new Chilkat.JsonObject();
resp.GetBodyJson(jsonResp);

jsonResp.EmitCompact = false;
Debug.WriteLine(jsonResp.Emit());

if (statusCode != 200) {
    Debug.WriteLine("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.
// 
Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadFromFile("qa_data/certs/chilkat_code_signing_2024.cer");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Chilkat.Rsa rsa = new Chilkat.Rsa();
// Tell the RSA object to use the cert's public key.
success = rsa.SetX509Cert(cert,false);
if (success == false) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

// Verify the signature using the cert's public key against the original string.
rsa.EncodingMode = "base64url";
bool valid = rsa.VerifyStringENC(signedString,"sha-256",jsonResp.StringOf("value"));
Debug.WriteLine("signature valid = " + Convert.ToString(valid));