(Java) Get XOAUTH2 Access Token from Google OAuth 2.0 Authorization Server

Obtains an OAUTH2 access token from the Google OAuth 2.0 Authorization Server. This is for Server to server applications using Google API's that need an access token. See https://developers.google.com/accounts/docs/OAuth2ServiceAccount

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

    CkHttp http = new CkHttp();

    // --------------------------------------------------------------------------------
    // For a step-by-step guide for setting up your Google Workspace service account,
    // see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
    // --------------------------------------------------------------------------------
    // Begin by loading your Google service account key (.p12)
    CkCert cert = new CkCert();
    boolean success = cert.LoadPfxFile("c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12","notasecret");
    if (success != true) {
        System.out.println(cert.lastErrorText());
        return;
        }

    // The ISS is your service account email address ending in gserviceaccount.com.
    String iss = "chilkatsvc@chilkat25.iam.gserviceaccount.com";

    // The scope is always the following string:
    String scope = "https://mail.google.com/";

    // The sub is your company email address
    String oauth_sub = "bob@yourcompany.com";

    // The access token is valid for this number of seconds.
    int numSec = 3600;

    String accessToken = http.g_SvcOauthAccessToken(iss,scope,oauth_sub,numSec,cert);
    if (http.get_LastMethodSuccess() != true) {
        System.out.println(http.lastErrorText());
        return;
        }
    else {
        System.out.println("access token: " + accessToken);
        }

    // The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.
  }
}