(Android™) 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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// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // 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.

    boolean success;

    // Provide information needed for Chilkat to automatically get an OAuth2 access token as needed.
    CkJsonObject 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"
    CkStringBuilder sb = new CkStringBuilder();
    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..

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

    CkHttp 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.
    String url = "https://VAULT_NAME.vault.azure.net/keys/{$certName}/{$certVersion}/sign?api-version=7.4";
    CkHttpResponse resp = http.PostJson3(url,"application/json",jsonBody);
    if (http.get_LastMethodSuccess() == false) {
        // This means something failed before we got a response.
        Log.i(TAG, http.lastErrorText());
        return;
        }

    int statusCode = resp.get_StatusCode();

    CkJsonObject jsonResp = new CkJsonObject();
    resp.GetBodyJson(jsonResp);

    jsonResp.put_EmitCompact(false);
    Log.i(TAG, jsonResp.emit());

    if (statusCode != 200) {
        Log.i(TAG, "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.
    // 
    CkCert cert = new CkCert();
    success = cert.LoadFromFile("qa_data/certs/chilkat_code_signing_2024.cer");
    if (success == false) {
        Log.i(TAG, cert.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();
    // Tell the RSA object to use the cert's public key.
    success = rsa.SetX509Cert(cert,false);
    if (success == false) {
        Log.i(TAG, rsa.lastErrorText());
        return;
        }

    // Verify the signature using the cert's public key against the original string.
    rsa.put_EncodingMode("base64url");
    boolean valid = rsa.VerifyStringENC(signedString,"sha-256",jsonResp.stringOf("value"));
    Log.i(TAG, "signature valid = " + String.valueOf(valid));

  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}