(Android™) Verify a Google JWT Using Google's Public Key

See more Google APIs Examples

Demonstrates how to verify a JWT that was signed using Google's RSA private key.

This example verifies the RSA signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

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

    CkHttp http = new CkHttp();
    CkStringBuilder sbPubKeys = new CkStringBuilder();

    boolean success = http.QuickGetSb("https://www.googleapis.com/oauth2/v3/certs",sbPubKeys);
    if (success == false) {
        Log.i(TAG, http.lastErrorText());
        return;
        }

    Log.i(TAG, sbPubKeys.getAsString());

    // Here are the keys:

    // {
    //   "keys": [
    //     {
    //       "e": "AQAB",
    //       "n": "4bAT6C6EeX8Dspje3FrAXw-nnhNk04e1RmNa4kjc0CHf6Pk7ryARlwA-6YilyPABqQfYHx60s8oSnxvUVprFfQ2-Q8aAZO7bPKSxnoGlcKERL2oLNA4Msvc89N9Y5ycThZUplf_QC19e6jyYXN6Nz-UnJSCLrtQY8tVhhVRs61j4A2N_p-enAi-r704Qi1-v-DKV4eVRkClKViploo8NyjUaT9L4vbBssPCjyimJzsWnEe1fED5c4LnHeArYzA_FEn3JJotqDIz9t2VnvZNTMhizHEX4VnORlEWMEfR8n4CEHQx7PcQUOmfqyw08gWeXQl1-uTjtIGaE-sRIv9u_vQ",
    //       "kty": "RSA",
    //       "use": "sig",
    //       "alg": "RS256",
    //       "kid": "2af90e87be140c20038898a6efa11283dab6031d"
    //     },
    //     {
    //       "n": "nzGsrziOYrMVYMpvUZOwkKNiPWcOPTYRYlDSdRW4UpAHdWPbPlyqaaphYhoMB5DXrVxI3bdvm7DOlo-sHNnulmAFQa-7TsQMxrZCvVdAbyXGID9DZYEqf8mkCV1Ohv7WY5lDUqlybIk1OSHdK7-1et0QS8nn-5LojGg8FK4ssLf3mV1APpujl27D1bDhyRb1MGumXYElwlUms7F9p9OcSp5pTevXCLmXs9MJJk4o9E1zzPpQ9Ko0lH9l_UqFpA7vwQhnw0nbh73rXOX2TUDCUqL4ThKU5Z9Pd-eZCEOatKe0mJTpQ00XGACBME_6ojCdfNIJr84Y_IpGKvkAEksn9w",
    //       "use": "sig",
    //       "kid": "87bbe0815b064e6d449cac999f0e50e72a3e4374",
    //       "e": "AQAB",
    //       "alg": "RS256",
    //       "kty": "RSA"
    //     }
    //   ]
    // }

    // -------------------------------------------------------------------------------------------
    // Replace this with your actual token.
    // This sample token contains a kid that does not match any of the above Google public keys.
    // -------------------------------------------------------------------------------------------
    String token = "eyJhbGciOiJSUzI1NiIsImtpZCI6IjQyZmY5MGQ3ZDM0OGM5NzM4MWE3YzExOWVmMWY1MzI0ZWEzZjViZWIifQ.eyJpc3MiOiJodHRwczovL2FjY291bnRzLmdvb2dsZS5jb20iLCJzdWIiOiIxMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExIiwiaWF0IjoxNjExMTE1MTQzLCJleHAiOjE2MTEyMDE1NDMsImF1ZCI6IjQyOTc1NzExNTE0ODg0OSJ9.pLem5i0bx3M7lJYj7jKv2Nq7c07X5YpZz-x1uM5RniW-v4LsX-lKIVvOq2x3-WoPqkzLXJfP0kG0dx1uD2q1NfFQK60YwKH4FnFtB6INnUP1dRVpP9_pTTKyAE28I3s5Tay4PbPdrCl7ZLCIJzCfpCW1TiWeVoPjp5HgZKTBHdP_sEkN_yO5dQerQXAkFJkV3kNgF9jI3ayT-KPqOIH6GVoWXjHFDyA2EYgJPEFRo5WSe6XycJ85p5duwT-OoBcb_kJZG9PxYd91eHlPCzp8vGxzIb2dVROCBxyM8e8W0cd9v15hfmpg9R-eG9vCM5y63ZLChZLFeHFx0Pd7hvAqfKg";

    CkJwt jwt = new CkJwt();
    String header = jwt.getHeader(token);

    Log.i(TAG, header);

    // Sample header:
    // {"alg":"RS256","kid":"87bbe0815b064e6d449cac999f0e50e72a3e4374"}

    // Load the public key matching the "kid" into a Chilkat public key object, then verify..

    CkJsonObject json = new CkJsonObject();
    json.Load(header);
    String kid = json.stringOf("kid");

    Log.i(TAG, "kid = " + kid);

    CkJsonObject jsonPubKeys = new CkJsonObject();
    jsonPubKeys.LoadSb(sbPubKeys);

    CkJsonObject jsonKey = jsonPubKeys.FindRecord("keys","kid",kid,true);
    if (jsonPubKeys.get_LastMethodSuccess() == false) {
        Log.i(TAG, "Did not find a matching public key based on the kid.");
        return;
        }

    Log.i(TAG, jsonKey.emit());

    // Load the matching public key into a Chilkat public key object.
    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromString(jsonKey.emit());

    if (success == false) {
        Log.i(TAG, pubKey.lastErrorText());
        return;
        }

    // ----------------------------------------------------------------------------------------
    // Now we can validate the JWT using Google's public key as shown in this example:
    // (Except we use the public key obtained as shown above instead of a public key loaded from a PEM file.
    // 
    // See Verify JWT Using an RSA Public Key

  }

  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."
  }
}