test: add attestation verifier integration tests

Author: josedab

streamline-client/src/test/java/io/streamline/attestation/AttestationVerifierTest.java

@@ -0,0 +1,60 @@
+package io.streamline.attestation;
+
+import org.junit.jupiter.api.Test;
+
+import java.nio.charset.StandardCharsets;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.PrivateKey;
+import java.security.Signature;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class AttestationVerifierTest {
+
+    private static class StubRecord implements AttestationVerifier.AttestedRecord {
+        final Map<String, byte[]> headers = new HashMap<>();
+        public String topic() { return "orders"; }
+        public int partition() { return 0; }
+        public long offset() { return 42L; }
+        public byte[] value() { return "{\"amount\":100}".getBytes(StandardCharsets.UTF_8); }
+        public long timestampMs() { return 1_700_000_000_000L; }
+        public int schemaId() { return 7; }
+        public String keyId() { return "broker-key-1"; }
+        public Map<String, byte[]> headers() { return headers; }
+    }
+
+    @Test
+    void verifies_valid_signature() throws Exception {
+        KeyPairGenerator kpg = KeyPairGenerator.getInstance("Ed25519");
+        KeyPair kp = kpg.generateKeyPair();
+        StubRecord r = new StubRecord();
+
+        Signature signer = Signature.getInstance("Ed25519");
+        signer.initSign(kp.getPrivate());
+        signer.update(AttestationVerifier.canonicalBytes(r));
+        byte[] sig = signer.sign();
+
+        r.headers.put(AttestationVerifier.HEADER, sig);
+        assertTrue(new AttestationVerifier(kp.getPublic()).verify(r));
+    }
+
+    @Test
+    void rejects_missing_header() throws Exception {
+        KeyPairGenerator kpg = KeyPairGenerator.getInstance("Ed25519");
+        KeyPair kp = kpg.generateKeyPair();
+        assertFalse(new AttestationVerifier(kp.getPublic()).verify(new StubRecord()));
+    }
+
+    @Test
+    void rejects_tampered_signature() throws Exception {
+        KeyPairGenerator kpg = KeyPairGenerator.getInstance("Ed25519");
+        KeyPair kp = kpg.generateKeyPair();
+        StubRecord r = new StubRecord();
+        r.headers.put(AttestationVerifier.HEADER, new byte[]{0x00, 0x01, 0x02});
+        assertFalse(new AttestationVerifier(kp.getPublic()).verify(r));
+    }
+}