Use a properly random source to generate digest client nonces

rt/transports/http/src/main/java/org/apache/cxf/transport/http/auth/DigestAuthSupplier.java

@@ -22,6 +22,7 @@
 import java.net.URI;
 import java.nio.ByteBuffer;
 import java.security.MessageDigest;
+import java.security.SecureRandom;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -36,6 +37,7 @@
  *
  */
 public class DigestAuthSupplier implements HttpAuthSupplier {
+    private static final SecureRandom CNONCE_GENERATOR = new SecureRandom();
 
     Map<URI, DigestInfo> authInfo = new ConcurrentHashMap<>();
 
@@ -107,8 +109,16 @@ private static String getAuthURI(URI currentURI) {
         return authURI;
     }
 
+    /**
+     * Creates the client nonce. RFC 7616 relies on the cnonce being unpredictable so
+     * that a hostile or spoofed server controlling the challenge nonce cannot steer
+     * the client into computing a digest over fully attacker-chosen input; a
+     * timestamp is guessable and must not be used here.
+     */
     public String createCnonce() {
-        return Long.toString(System.currentTimeMillis());
+        byte[] bytes = new byte[16];
+        CNONCE_GENERATOR.nextBytes(bytes);
+        return StringUtils.toHexString(bytes);
     }
 
     class DigestInfo {

rt/transports/http/src/test/java/org/apache/cxf/transport/http/auth/DigestAuthSupplierTest.java

@@ -29,6 +29,7 @@
 import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
 
 public class DigestAuthSupplierTest {
@@ -92,6 +93,19 @@ public String createCnonce() {
         assertEquals(expectedParams, params);
     }
 
+    @Test
+    public void testCnonceIsUnpredictable() throws Exception {
+        DigestAuthSupplier authSupplier = new DigestAuthSupplier();
+        String cnonce1 = authSupplier.createCnonce();
+        String cnonce2 = authSupplier.createCnonce();
+        // 16 random bytes, hex encoded
+        assertEquals(32, cnonce1.length());
+        assertTrue(cnonce1.matches("[0-9a-fA-F]+"));
+        assertNotEquals(cnonce1, cnonce2);
+        // must not be an epoch-millis timestamp
+        assertNotEquals(Long.toString(System.currentTimeMillis()).length(), cnonce1.length());
+    }
+
     @Test
     public void testUrlEncodedUri() throws Exception {
         AuthorizationPolicy authPolicy = new AuthorizationPolicy();