GoogleCloudPlatform · jabubake · Aug 15, 2017 · Aug 15, 2017 · Aug 15, 2017 · Aug 15, 2017
diff --git a/iap/README.md b/iap/README.md
@@ -46,7 +46,7 @@ It will be used to test both the authorization of an incoming request to an IAP
   ```
 
 ## References
-- [JWT library for Java (jjwt)](https://github.com/jwtk/jjwt)
+- [Nimbus JOSE jwt library](https://bitbucket.org/connect2id/nimbus-jose-jwt/wiki/Home)
 - [Cloud IAP docs](https://cloud.google.com/iap/docs/)
 - [Service account credentials](https://cloud.google.com/docs/authentication#getting_credentials_for_server-centric_flow)
 

diff --git a/iap/pom.xml b/iap/pom.xml
@@ -52,17 +52,16 @@
       <artifactId>javax.servlet-api</artifactId>
       <version>3.1.0</version>
     </dependency>
-
     <!-- [START dependencies] -->
     <dependency>
       <groupId>com.google.auth</groupId>
       <artifactId>google-auth-library-oauth2-http</artifactId>
       <version>0.7.1</version>
     </dependency>
     <dependency>
-      <groupId>io.jsonwebtoken</groupId>
-      <artifactId>jjwt</artifactId>
-      <version>0.7.0</version>
+      <groupId>com.nimbusds</groupId>
+      <artifactId>nimbus-jose-jwt</artifactId>
+      <version>4.41.1</version>
     </dependency>
     <!-- [END dependencies] -->
 

diff --git a/iap/src/main/java/com/example/iap/BuildIapRequest.java b/iap/src/main/java/com/example/iap/BuildIapRequest.java
@@ -11,7 +11,9 @@
  * express or implied. See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package com.example.iap;
+// [START generate_iap_request]
 
 import com.google.api.client.http.GenericUrl;
 import com.google.api.client.http.HttpHeaders;
@@ -26,18 +28,18 @@
 import com.google.api.client.util.GenericData;
 import com.google.auth.oauth2.GoogleCredentials;
 import com.google.auth.oauth2.ServiceAccountCredentials;
-import io.jsonwebtoken.Jwts;
-import io.jsonwebtoken.SignatureAlgorithm;
-
-import java.io.IOException;
-import java.net.URL;
+import com.nimbusds.jose.JWSAlgorithm;
+import com.nimbusds.jose.JWSHeader;
+import com.nimbusds.jose.JWSSigner;
+import com.nimbusds.jose.crypto.RSASSASigner;
+import com.nimbusds.jwt.JWTClaimsSet;
+import com.nimbusds.jwt.SignedJWT;
 import java.time.Clock;
 import java.time.Instant;
 import java.util.Collections;
 import java.util.Date;
 
 public class BuildIapRequest {
-  // [START generate_iap_request]
   private static final String IAM_SCOPE = "https://www.googleapis.com/auth/iam";
   private static final String OAUTH_TOKEN_URI = "https://www.googleapis.com/oauth2/v4/token";
   private static final String JWT_BEARER_TOKEN_GRANT_TYPE =
@@ -60,22 +62,33 @@ private static ServiceAccountCredentials getCredentials() throws Exception {
     return (ServiceAccountCredentials) credentials;
   }
 
-  private static String getSignedJWToken(ServiceAccountCredentials credentials, String iapClientId)
-      throws IOException {
+  private static String getSignedJwt(ServiceAccountCredentials credentials, String iapClientId)
+      throws Exception {
     Instant now = Instant.now(clock);
     long expirationTime = now.getEpochSecond() + EXPIRATION_TIME_IN_SECONDS;
 
     // generate jwt signed by service account
-    return Jwts.builder()
-        .setHeaderParam("kid", credentials.getPrivateKeyId())
-        .setIssuer(credentials.getClientEmail())
-        .setAudience(OAUTH_TOKEN_URI)
-        .setSubject(credentials.getClientEmail())
-        .setIssuedAt(Date.from(now))
-        .setExpiration(Date.from(Instant.ofEpochSecond(expirationTime)))
-        .claim("target_audience", iapClientId)
-        .signWith(SignatureAlgorithm.RS256, credentials.getPrivateKey())
-        .compact();
+    // header must contain algorithm ("alg") and key ID ("kid")
+    JWSHeader jwsHeader =
+        new JWSHeader.Builder(JWSAlgorithm.RS256).keyID(credentials.getPrivateKeyId()).build();
+
+    // set required claims
+    JWTClaimsSet claims =
+        new JWTClaimsSet.Builder()
+            .audience(OAUTH_TOKEN_URI)
+            .issuer(credentials.getClientEmail())
+            .subject(credentials.getClientEmail())
+            .issueTime(Date.from(now))
+            .expirationTime(Date.from(Instant.ofEpochSecond(expirationTime)))
+            .claim("target_audience", iapClientId)
+            .build();
+
+    // sign using service account private key
+    JWSSigner signer = new RSASSASigner(credentials.getPrivateKey());
+    SignedJWT signedJwt = new SignedJWT(jwsHeader, claims);
+    signedJwt.sign(signer);
+
+    return signedJwt.serialize();
   }
 
   private static String getGoogleIdToken(String jwt) throws Exception {
@@ -100,16 +113,18 @@ private static String getGoogleIdToken(String jwt) throws Exception {
 
   /**
    * Clone request and add an IAP Bearer Authorization header with signed JWT token.
+   *
    * @param request Request to add authorization header
    * @param iapClientId OAuth 2.0 client ID for IAP protected resource
    * @return Clone of request with Bearer style authorization header with signed jwt token.
-   * @throws Exception
+   * @throws Exception exception creating signed JWT
    */
-  public static HttpRequest buildIAPRequest(HttpRequest request, String iapClientId) throws Exception {
+  public static HttpRequest buildIapRequest(HttpRequest request, String iapClientId)
+      throws Exception {
     // get service account credentials
     ServiceAccountCredentials credentials = getCredentials();
     // get the base url of the request URL
-    String jwt = getSignedJWToken(credentials, iapClientId);
+    String jwt = getSignedJwt(credentials, iapClientId);
     if (jwt == null) {
       throw new Exception(
           "Unable to create a signed jwt token for : "
@@ -132,5 +147,5 @@ public static HttpRequest buildIAPRequest(HttpRequest request, String iapClientI
         .buildRequest(request.getRequestMethod(), request.getUrl(), request.getContent())
         .setHeaders(httpHeaders);
   }
-  // [END generate_iap_request]
 }
+// [END generate_iap_request]
diff --git a/iap/src/main/java/com/example/iap/VerifyIapRequestHeader.java b/iap/src/main/java/com/example/iap/VerifyIapRequestHeader.java
@@ -11,162 +11,121 @@
  * express or implied. See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package com.example.iap;
+// [START verify_iap_request]
 
-import com.fasterxml.jackson.core.type.TypeReference;
-import com.fasterxml.jackson.databind.ObjectMapper;
-import com.google.api.client.http.GenericUrl;
 import com.google.api.client.http.HttpRequest;
-import com.google.api.client.http.HttpResponse;
-import com.google.api.client.http.HttpStatusCodes;
-import com.google.api.client.http.javanet.NetHttpTransport;
-import com.google.api.client.util.PemReader;
-import com.google.api.client.util.PemReader.Section;
-import io.jsonwebtoken.Claims;
-import io.jsonwebtoken.JwsHeader;
-import io.jsonwebtoken.Jwt;
-import io.jsonwebtoken.Jwts;
-import io.jsonwebtoken.SigningKeyResolver;
-import io.jsonwebtoken.impl.DefaultClaims;
-
-import java.io.IOException;
-import java.io.StringReader;
-import java.security.Key;
-import java.security.KeyFactory;
-import java.security.NoSuchAlgorithmException;
-import java.security.PublicKey;
+import com.google.common.base.Preconditions;
+import com.nimbusds.jose.JWSHeader;
+import com.nimbusds.jose.JWSVerifier;
+import com.nimbusds.jose.crypto.ECDSAVerifier;
+import com.nimbusds.jose.jwk.ECKey;
+import com.nimbusds.jose.jwk.JWK;
+import com.nimbusds.jose.jwk.JWKSet;
+import com.nimbusds.jwt.JWTClaimsSet;
+import com.nimbusds.jwt.SignedJWT;
+import java.net.URL;
 import java.security.interfaces.ECPublicKey;
-import java.security.spec.InvalidKeySpecException;
-import java.security.spec.X509EncodedKeySpec;
+import java.time.Clock;
+import java.time.Instant;
+import java.util.Date;
 import java.util.HashMap;
 import java.util.Map;
 
 /** Verify IAP authorization JWT token in incoming request. */
 public class VerifyIapRequestHeader {
 
-  // [START verify_iap_request]
   private static final String PUBLIC_KEY_VERIFICATION_URL =
-      "https://www.gstatic.com/iap/verify/public_key";
+      "https://www.gstatic.com/iap/verify/public_key-jwk";
+
   private static final String IAP_ISSUER_URL = "https://cloud.google.com/iap";
 
-  private final Map<String, Key> keyCache = new HashMap<>();
-  private final ObjectMapper mapper = new ObjectMapper();
-  private final TypeReference<HashMap<String, String>> typeRef =
-      new TypeReference<HashMap<String, String>>() {};
-
-  private SigningKeyResolver resolver =
-      new SigningKeyResolver() {
-        @Override
-        public Key resolveSigningKey(JwsHeader header, Claims claims) {
-          return resolveSigningKey(header);
-        }
-
-        @Override
-        public Key resolveSigningKey(JwsHeader header, String payload) {
-          return resolveSigningKey(header);
-        }
-
-        private Key resolveSigningKey(JwsHeader header) {
-          String keyId = header.getKeyId();
-          Key key = keyCache.get(keyId);
-          if (key != null) {
-            return key;
-          }
-          try {
-            HttpRequest request =
-                new NetHttpTransport()
-                    .createRequestFactory()
-                    .buildGetRequest(new GenericUrl(PUBLIC_KEY_VERIFICATION_URL));
-            HttpResponse response = request.execute();
-            if (response.getStatusCode() != HttpStatusCodes.STATUS_CODE_OK) {
-              return null;
-            }
-            Map<String, String> keys = mapper.readValue(response.parseAsString(), typeRef);
-            for (Map.Entry<String, String> keyData : keys.entrySet()) {
-              if (!keyData.getKey().equals(keyId)) {
-                continue;
-              }
-              key = getKey(keyData.getValue());
-              if (key != null) {
-                keyCache.putIfAbsent(keyId, key);
-              }
-            }
-
-          } catch (IOException e) {
-            // ignore exception
-          }
-          return key;
-        }
-      };
+  // using a simple cache with no eviction for this sample
+  private final Map<String, JWK> keyCache = new HashMap<>();
+
+  private static Clock clock = Clock.systemUTC();
+
+  private ECPublicKey getKey(String kid, String alg) throws Exception {
+    JWK jwk = keyCache.get(kid);
+    if (jwk == null) {
+      // update cache loading jwk public key data from url
+      JWKSet jwkSet = JWKSet.load(new URL(PUBLIC_KEY_VERIFICATION_URL));
+      for (JWK key : jwkSet.getKeys()) {
+        keyCache.put(key.getKeyID(), key);
+      }
+      jwk = keyCache.get(kid);
+    }
+    // confirm that algorithm matches
+    if (jwk != null && jwk.getAlgorithm().getName().equals(alg)) {
+      return ECKey.parse(jwk.toJSONString()).toECPublicKey();
+    }
+    return null;
+  }
 
   // Verify jwt tokens addressed to IAP protected resources on App Engine.
-  // The project *number* for your Google Cloud project available via 'gcloud projects describe $PROJECT_ID'
-  // or in the Project Info card in Cloud Console.
+  // The project *number* for your Google Cloud project via 'gcloud projects describe $PROJECT_ID'
+  // The project *number* can also be retrieved from the Project Info card in Cloud Console.
   // projectId is The project *ID* for your Google Cloud Project.
-  Jwt verifyJWTTokenForAppEngine(HttpRequest request, long projectNumber, String projectId) throws Exception {
+  boolean verifyJwtForAppEngine(HttpRequest request, long projectNumber, String projectId)
+      throws Exception {
     // Check for iap jwt header in incoming request
-    String jwtToken =
-        request.getHeaders().getFirstHeaderStringValue("x-goog-iap-jwt-assertion");
-    if (jwtToken == null) {
-      return null;
+    String jwt = request.getHeaders().getFirstHeaderStringValue("x-goog-iap-jwt-assertion");
+    if (jwt == null) {
+      return false;
     }
-    return verifyJWTToken(jwtToken, String.format("/projects/%s/apps/%s",
-                                                  Long.toUnsignedString(projectNumber),
-                                                 projectId));
+    return verifyJwt(
+        jwt,
+        String.format("/projects/%s/apps/%s", Long.toUnsignedString(projectNumber), projectId));
   }
 
-  Jwt verifyJWTTokenForComputeEngine(HttpRequest request, long projectNumber, long backendServiceId) throws Exception {
+  boolean verifyJwtForComputeEngine(
+      HttpRequest request, long projectNumber, long backendServiceId) throws Exception {
     // Check for iap jwt header in incoming request
-    String jwtToken =
-        request.getHeaders().getFirstHeaderStringValue("x-goog-iap-jwt-assertion");
+    String jwtToken = request.getHeaders()
+        .getFirstHeaderStringValue("x-goog-iap-jwt-assertion");
     if (jwtToken == null) {
-      return null;
-    }
-    return verifyJWTToken(jwtToken, String.format("/projects/%s/global/backendServices/%s",
-                                                  Long.toUnsignedString(projectNumber),
-                                                  Long.toUnsignedString(backendServiceId)));
-  }
-
-  Jwt verifyJWTToken(String jwtToken, String expectedAudience) throws Exception {
-    // Time constraints are automatically checked, use setAllowedClockSkewSeconds
-    // to specify a leeway window
-    // The token was issued in a past date "iat" < TODAY
-    // The token hasn't expired yet "exp" > TODAY
-    Jwt jwt =
-        Jwts.parser()
-            .setSigningKeyResolver(resolver)
-            .requireAudience(expectedAudience)
-            .requireIssuer(IAP_ISSUER_URL)
-            .parse(jwtToken);
-    DefaultClaims claims = (DefaultClaims) jwt.getBody();
-    if (claims.getSubject() == null) {
-      throw new Exception("Subject expected, not found.");
+      return false;
     }
-    if (claims.get("email") == null) {
-      throw new Exception("Email expected, not found.");
-    }
-    return jwt;
+    return verifyJwt(
+        jwtToken,
+        String.format(
+            "/projects/%s/global/backendServices/%s",
+            Long.toUnsignedString(projectNumber), Long.toUnsignedString(backendServiceId)));
   }
 
-  private ECPublicKey getKey(String keyText) throws IOException {
-    StringReader reader = new StringReader(keyText);
-    Section section = PemReader.readFirstSectionAndClose(reader, "PUBLIC KEY");
-    if (section == null) {
-      throw new IOException("Invalid data.");
-    } else {
-      byte[] bytes = section.getBase64DecodedBytes();
-      X509EncodedKeySpec keySpec = new X509EncodedKeySpec(bytes);
-      try {
-        KeyFactory kf = KeyFactory.getInstance("EC");
-        PublicKey publicKey = kf.generatePublic(keySpec);
-        if (publicKey instanceof ECPublicKey) {
-          return (ECPublicKey) publicKey;
-        }
-      } catch (InvalidKeySpecException | NoSuchAlgorithmException var7) {
-        throw new IOException("Unexpected exception reading data", var7);
-      }
-    }
-    return null;
+  private boolean verifyJwt(String jwtToken, String expectedAudience) throws Exception {
+
+    // parse signed token into header / claims
+    SignedJWT signedJwt = SignedJWT.parse(jwtToken);
+    JWSHeader jwsHeader = signedJwt.getHeader();
+
+    // header must have algorithm("alg") and "kid"
+    Preconditions.checkNotNull(jwsHeader.getAlgorithm());
+    Preconditions.checkNotNull(jwsHeader.getKeyID());
+
+    JWTClaimsSet claims = signedJwt.getJWTClaimsSet();
+
+    // claims must have audience, issuer
+    Preconditions.checkArgument(claims.getAudience().contains(expectedAudience));
+    Preconditions.checkArgument(claims.getIssuer().equals(IAP_ISSUER_URL));
+
+    // claim must have issued at time in the past
+    Date currentTime = Date.from(Instant.now(clock));
+    Preconditions.checkArgument(claims.getIssueTime().before(currentTime));
+    // claim must have expiration time in the future
+    Preconditions.checkArgument(claims.getExpirationTime().after(currentTime));
+
+    // must have subject, email
+    Preconditions.checkNotNull(claims.getSubject());
+    Preconditions.checkNotNull(claims.getClaim("email"));
+
+    // verify using public key : lookup with key id, algorithm name provided
+    ECPublicKey publicKey = getKey(jwsHeader.getKeyID(), jwsHeader.getAlgorithm().getName());
+
+    Preconditions.checkNotNull(publicKey);
+    JWSVerifier jwsVerifier = new ECDSAVerifier(publicKey);
+    return signedJwt.verify(jwsVerifier);
   }
-  // [END verify_iap_request]
 }
+// [END verify_iap_request]