Настоящая почта: docker-compose.public.yml (MX, DKIM, Let's Encrypt через lego), сертификат перечитывается без перезапуска

- ReloadingKeyManager: сертификат и ключ из PEM (PKCS#8, RSA, EC/SEC1 как у lego), раз в минуту
  проверяет файлы и перечитывает их; битый файл оставляет прежний сертификат; поколения по алиасам.
- docker-compose.public.yml: порты 25/587/465/993 на публичном адресе ВМ, OUTBOUND_MODE=mx, DKIM,
  SPF/DMARC, регистрация закрыта, без ловушки; сервис acme (lego v5.5.2, HTTP-01 на :80, EC256,
  продление за 30 дней, хук кладёт пару в том tls для uid 10001).
- README: раздел «Настоящая почта», DNS-записи, перечитка сертификата.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/test/java/com/mailserver/smtp/ReloadingKeyManagerTest.java

@@ -0,0 +1,149 @@
+package com.mailserver.smtp;
+
+import org.bouncycastle.asn1.x500.X500Name;
+import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
+import org.bouncycastle.cert.jcajce.JcaX509v3CertificateBuilder;
+import org.bouncycastle.openssl.jcajce.JcaPEMWriter;
+import org.bouncycastle.operator.jcajce.JcaContentSignerBuilder;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.StringWriter;
+import java.math.BigInteger;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.FileTime;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.cert.X509Certificate;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.util.Date;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ReloadingKeyManagerTest {
+
+    /** A clock moved by hand */
+    static final class TestClock extends Clock {
+        Instant now = Instant.parse("2026-11-06T12:00:00Z");
+
+        @Override
+        public ZoneOffset getZone() {
+            return ZoneOffset.UTC;
+        }
+
+        @Override
+        public Clock withZone(java.time.ZoneId zone) {
+            return this;
+        }
+
+        @Override
+        public Instant instant() {
+            return now;
+        }
+    }
+
+    @Test
+    void readsTheFilesAgainWhenTheyChange(@TempDir Path dir) throws Exception {
+        Path cert = dir.resolve("cert.pem");
+        Path key = dir.resolve("key.pem");
+        SmtpTls.selfSigned("old.example", cert, key);
+        TestClock clock = new TestClock();
+        ReloadingKeyManager manager = new ReloadingKeyManager(cert, key, Duration.ofMinutes(1), clock);
+
+        String first = manager.chooseEngineServerAlias("RSA", null, null);
+        assertEquals("CN=old.example", subject(manager.getCertificateChain(first)));
+        assertNull(manager.chooseEngineServerAlias("EC", null, null), "an RSA key is not offered for EC");
+
+        SmtpTls.selfSigned("new.example", cert, key);
+        Files.setLastModifiedTime(cert, FileTime.from(Instant.now().plusSeconds(5)));
+        Files.setLastModifiedTime(key, FileTime.from(Instant.now().plusSeconds(5)));
+
+        assertEquals(first, manager.chooseEngineServerAlias("RSA", null, null), "not checked before the interval");
+
+        clock.now = clock.now.plus(Duration.ofMinutes(1));
+        String second = manager.chooseEngineServerAlias("RSA", null, null);
+        assertNotEquals(first, second);
+        assertEquals("CN=new.example", subject(manager.getCertificateChain(second)));
+        assertNotNull(manager.getPrivateKey(second));
+        assertNotNull(manager.getCertificateChain(first), "a handshake that holds the previous alias still finishes");
+    }
+
+    @Test
+    void keepsTheOldCertificateWhenTheNewFileIsBroken(@TempDir Path dir) throws Exception {
+        Path cert = dir.resolve("cert.pem");
+        Path key = dir.resolve("key.pem");
+        SmtpTls.selfSigned("old.example", cert, key);
+        TestClock clock = new TestClock();
+        ReloadingKeyManager manager = new ReloadingKeyManager(cert, key, Duration.ofMinutes(1), clock);
+
+        Files.writeString(cert, "-----BEGIN CERTIFICATE-----\nhalf");
+        Files.setLastModifiedTime(cert, FileTime.from(Instant.now().plusSeconds(5)));
+        clock.now = clock.now.plus(Duration.ofMinutes(2));
+
+        String alias = manager.chooseEngineServerAlias("RSA", null, null);
+        assertEquals("CN=old.example", subject(manager.getCertificateChain(alias)));
+    }
+
+    @Test
+    void readsTraditionalEcKeysAsLegoWritesThem(@TempDir Path dir) throws Exception {
+        KeyPairGenerator generator = KeyPairGenerator.getInstance("EC");
+        generator.initialize(256);
+        KeyPair pair = generator.generateKeyPair();
+        X500Name name = new X500Name("CN=mail.example");
+        X509Certificate certificate = new JcaX509CertificateConverter().getCertificate(
+                new JcaX509v3CertificateBuilder(name, BigInteger.ONE, new Date(System.currentTimeMillis() - 86_400_000L),
+                        new Date(System.currentTimeMillis() + 86_400_000L), name, pair.getPublic())
+                        .build(new JcaContentSignerBuilder("SHA256withECDSA").build(pair.getPrivate())));
+        Path cert = dir.resolve("cert.pem");
+        Path key = dir.resolve("key.pem");
+        Files.writeString(cert, pem(certificate));
+        Files.writeString(key, sec1(pair)); // -----BEGIN EC PRIVATE KEY----- (SEC1 with the curve), not PKCS#8
+        assertTrue(Files.readString(key).contains("EC PRIVATE KEY"));
+
+        ReloadingKeyManager manager = new ReloadingKeyManager(cert, key, Duration.ofMinutes(1), new TestClock());
+        String alias = manager.chooseEngineServerAlias("EC", null, null);
+        assertNotNull(alias);
+        assertEquals("EC", manager.getPrivateKey(alias).getAlgorithm());
+        assertNull(manager.chooseEngineServerAlias("RSA", null, null));
+    }
+
+    @Test
+    void refusesAKeyThatDoesNotMatchTheCertificateType(@TempDir Path dir) throws Exception {
+        Path cert = dir.resolve("cert.pem");
+        Path key = dir.resolve("key.pem");
+        SmtpTls.selfSigned("rsa.example", cert, key);
+        KeyPairGenerator generator = KeyPairGenerator.getInstance("EC");
+        generator.initialize(256);
+        Files.writeString(key, sec1(generator.generateKeyPair()));
+        assertThrows(IllegalStateException.class,
+                () -> new ReloadingKeyManager(cert, key, Duration.ofMinutes(1), new TestClock()));
+    }
+
+    /** As lego and openssl ecparam -genkey write it: SEC1 with the named curve secp256r1 */
+    private static String sec1(KeyPair pair) throws Exception {
+        java.security.interfaces.ECPrivateKey key = (java.security.interfaces.ECPrivateKey) pair.getPrivate();
+        org.bouncycastle.asn1.sec.ECPrivateKey sec1 = new org.bouncycastle.asn1.sec.ECPrivateKey(256, key.getS(),
+                new org.bouncycastle.asn1.x9.X962Parameters(org.bouncycastle.asn1.sec.SECObjectIdentifiers.secp256r1));
+        StringWriter out = new StringWriter();
+        try (org.bouncycastle.util.io.pem.PemWriter writer = new org.bouncycastle.util.io.pem.PemWriter(out)) {
+            writer.writeObject(new org.bouncycastle.util.io.pem.PemObject("EC PRIVATE KEY", sec1.getEncoded()));
+        }
+        return out.toString();
+    }
+
+    private static String subject(X509Certificate[] chain) {
+        return chain[0].getSubjectX500Principal().getName();
+    }
+
+    private static String pem(Object object) throws Exception {
+        StringWriter out = new StringWriter();
+        try (JcaPEMWriter writer = new JcaPEMWriter(out)) {
+            writer.writeObject(object);
+        }
+        return out.toString();
+    }
+}