/*
* Copyright 2016 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.appengine.appidentity;
import com.google.appengine.api.appidentity.AppIdentityService;
import com.google.appengine.api.appidentity.AppIdentityServiceFactory;
import com.google.appengine.api.appidentity.PublicCertificate;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.util.Arrays;
import java.util.Collection;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@SuppressWarnings("serial")
public class SignForAppServlet extends HttpServlet {
private final AppIdentityService appIdentity;
public SignForAppServlet() {
appIdentity = AppIdentityServiceFactory.getAppIdentityService();
}
// [START asserting_identity_to_other_services]
// Note that the algorithm used by AppIdentity.signForApp() and
// getPublicCertificatesForApp() is "SHA256withRSA"
private byte[] signBlob(byte[] blob) {
AppIdentityService.SigningResult result = appIdentity.signForApp(blob);
return result.getSignature();
}
private byte[] getPublicCertificate() throws UnsupportedEncodingException {
Collection<PublicCertificate> certs = appIdentity.getPublicCertificatesForApp();
PublicCertificate publicCert = certs.iterator().next();
return publicCert.getX509CertificateInPemFormat().getBytes("UTF-8");
}
private Certificate parsePublicCertificate(byte[] publicCert)
throws CertificateException, NoSuchAlgorithmException {
InputStream stream = new ByteArrayInputStream(publicCert);
CertificateFactory cf = CertificateFactory.getInstance("X.509");
return cf.generateCertificate(stream);
}
private boolean verifySignature(byte[] blob, byte[] blobSignature, PublicKey pk)
throws NoSuchAlgorithmException, InvalidKeyException, SignatureException {
Signature signature = Signature.getInstance("SHA256withRSA");
signature.initVerify(pk);
signature.update(blob);
return signature.verify(blobSignature);
}
private String simulateIdentityAssertion()
throws CertificateException, UnsupportedEncodingException, NoSuchAlgorithmException,
InvalidKeyException, SignatureException {
// Simulate the sending app.
String message = "abcdefg";
byte[] blob = message.getBytes();
byte[] blobSignature = signBlob(blob);
byte[] publicCert = getPublicCertificate();
// Simulate the receiving app, which gets the certificate, blob, and signature.
Certificate cert = parsePublicCertificate(publicCert);
PublicKey pk = cert.getPublicKey();
boolean isValid = verifySignature(blob, blobSignature, pk);
return String.format(
"isValid=%b for message: %s\n\tsignature: %s\n\tpublic cert: %s",
isValid,
message,
Arrays.toString(blobSignature),
Arrays.toString(publicCert));
}
// [END asserting_identity_to_other_services]
@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
resp.setContentType("text/plain");
try {
resp.getWriter().println(simulateIdentityAssertion());
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}