(Java) PRODA Get OAuth2 Access Token using JWT

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Demonstrates how to get an OAuth2 access token for the PRODA Australian Government Online Services using a JWT.

For more information, see https://www.servicesaustralia.gov.au/organisations/business/services/proda-provider-digital-access

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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 create a JWT to be sent in the POST to https://vnd.proda.humanservices.gov.au/mga/sps/oauth/oauth20/token

    CkPrivateKey privKey = new CkPrivateKey();

    // Load an RSA private key from a PEM file.
    // Chilkat provides alternative methods to load from other formats, or to load from a string or binary data.
    boolean success = privKey.LoadEncryptedPemFile("qa_data/pem/rsa_passwd.pem","passwd");
    if (success != true) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    CkJwt jwt = new CkJwt();

    // Build the JOSE header
    CkJsonObject jose = new CkJsonObject();
    // Use RS256.  Pass the string "RS384" or "RS512" to use RSA with SHA-384 or SHA-512.
    success = jose.AppendString("alg","RS256");
    success = jose.AppendString("typ","JWT");
    success = jose.AppendString("kid","test-device");

    // Now build the JWT claims (also known as the payload)
    CkJsonObject claims = new CkJsonObject();
    success = claims.AppendString("iss","9646844092");
    success = claims.AppendString("sub","test-device");
    success = claims.AppendString("aud","https://proda.humanservices.gov.au");

    // Set the timestamp of when the JWT was created to now.
    int curDateTime = jwt.GenNumericDate(0);
    success = claims.AddIntAt(-1,"iat",curDateTime);

    // Set the timestamp defining an expiration time (end time) for the token
    // to be now + 1 hour (3600 seconds)
    success = claims.AddIntAt(-1,"exp",curDateTime+3600);

    // Produce the smallest possible JWT:
    jwt.put_AutoCompact(true);

    // Create the JWT token.  This is where the RSA signature is created.
    String jwtToken = jwt.createJwtPk(jose.emit(),claims.emit(),privKey);

    // ---------------------------------------------------------------------
    // Build and send the POST, which should look something like this:

    // POST https://vnd.proda.humanservices.gov.au/mga/sps/oauth/oauth20/token HTTP/1.1
    // Content-Type: application/x-www-form-urlencoded
    // Content-Length: 666
    // Host: vnd.proda.humanservices.gov.au
    // 
    // grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&assertion=<jwt>&client_id=VendorClient03

    CkHttp http = new CkHttp();

    CkHttpRequest req = new CkHttpRequest();

    // Add the request params.
    req.AddParam("grant_type","urn:ietf:params:oauth:grant-type:jwt-bearer");
    req.AddParam("assertion",jwtToken);
    req.AddParam("client_id","VendorClient03");

    // Send the POST
    // Chilkat automatically adds the Content-Type (which is application/x-www-form-urlencoded for the PostUrlEncoded method)
    // Chilkat also automatically adds the Host and Content-Length headers.
    CkHttpResponse resp;
    resp = http.PostUrlEncoded("https://vnd.proda.humanservices.gov.au/mga/sps/oauth/oauth20/token",req);
    if (http.get_LastMethodSuccess() != true) {
        System.out.println(http.lastErrorText());
        return;
        }

    System.out.println("Response status code = " + resp.get_StatusCode());
    System.out.println("Response body:");
    System.out.println(resp.bodyStr());
  }
}