(Java) Get Google API Access Token using JSON Private Key using NIST Time Server Date/Time

Demonstrates how to get a Google API access token using a JSON service account private key, using the NIST time server date/time rather than the local system date/time.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // First, let's get the current date/time from time-c.nist.gov
    CkSocket socket = new CkSocket();

    // Connect to an NIST time server and read the current date/time
    int maxWaitMs = 8000;
    boolean useTls = false;
    boolean success = socket.Connect("time-c.nist.gov",37,useTls,maxWaitMs);
    if (success != true) {
        System.out.println(socket.lastErrorText());
        return;
        }

    // The time server will send a big-endian 32-bit integer representing
    // the number of seconds since since 00:00 (midnight) 1 January 1900 GMT.
    // The ReceiveInt32 method will receive a 4-byte integer, but returns
    // true or false to indicate success.  If successful, the integer
    // is obtained via the ReceivedInt property.
    boolean bigEndian = true;
    success = socket.ReceiveInt32(bigEndian);
    if (success != true) {
        System.out.println(socket.lastErrorText());
        return;
        }

    CkDateTime dt = new CkDateTime();
    dt.SetFromNtpTime(socket.get_ReceivedInt());

    // Show the current local date/time
    boolean bLocalTime = true;
    System.out.println("Current local date/time: " + dt.getAsRfc822(bLocalTime));

    maxWaitMs = 10;
    socket.Close(maxWaitMs);

    // ------------------------------------------------------------------------
    // OK, we have the current date/time.  We'll use it to set the IAT property
    // in the code below.

    // First load the JSON key into a string.
    CkFileAccess fac = new CkFileAccess();
    String jsonKey = fac.readEntireTextFile("qa_data/googleApi/ChilkatTest-ab2ecd52ef98.json","utf-8");
    if (fac.get_LastMethodSuccess() != true) {
        System.out.println(fac.lastErrorText());
        return;
        }

    // A JSON private key should look like this:

    // 	{
    // 	  "type": "service_account",
    // 	  "project_id": "chilkattest-1350",
    // 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
    // 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
    // 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
    // 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
    // 	  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    // 	  "token_uri": "https://accounts.google.com/o/oauth2/token",
    // 	  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    // 	  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
    // 	}

    CkAuthGoogle gAuth = new CkAuthGoogle();
    gAuth.put_JsonKey(jsonKey);

    // Choose a scope.
    gAuth.put_Scope("https://www.googleapis.com/auth/cloud-platform");

    // Request an access token that is valid for this many seconds.
    gAuth.put_ExpireNumSeconds(3600);

    // If the application is requesting delegated access:
    // The email address of the user for which the application is requesting delegated access,
    // then set the email address here. (Otherwise leave it empty.)
    gAuth.put_SubEmailAddress("");

    // ------------------------------------------------------------------------
    // Set the IAT using the date/time from the NIST time server.
    int unixTime = dt.GetAsUnixTime(false);
    System.out.println("unixTime = " + unixTime);
    gAuth.put_Iat(unixTime);

    // Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
    // The Chilkat socket object is used so that the connection can be established
    // through proxies or an SSH tunnel if desired.
    CkSocket tlsSock = new CkSocket();
    boolean success = tlsSock.Connect("www.googleapis.com",443,true,5000);
    if (success != true) {
        System.out.println(tlsSock.lastErrorText());
        return;
        }

    // Send the request to obtain the access token.
    success = gAuth.ObtainAccessToken(tlsSock);
    if (success != true) {
        System.out.println(gAuth.lastErrorText());
        return;
        }

    // Examine the access token:
    System.out.println("Access Token: " + gAuth.accessToken());
  }
}