use the SAN type tag in Mbed TLS verify_hostname and get_cert_sans (#2614)

* use the SAN type tag in Mbed TLS verify_hostname and get_cert_sans

Mbed TLS keeps a subjectAltName entry's GeneralName tag in buf.tag and the bare value in buf.p / buf.len. verify_hostname ignored the tag, so a dNSName whose bytes equal an address authenticated that IP host, and an iPAddress or rfc822Name was matched as a DNS pattern. get_cert_sans looked for the tag inside the value, so it reported no entries for an ordinary certificate, or part of a dNSName as an entry of its own.

* Shorten the SAN type comments

---------

Co-authored-by: yhirose <yuji.hirose.bug@gmail.com>

test/test.cc

@@ -42,6 +42,7 @@ inline std::string u8_to_string(const char8_t *s) {
 #define SERVER_CERT2_FILE "./cert2.pem"
 #define SERVER_CERT_IP_CN_FILE "./cert_ip_cn.pem"
 #define SERVER_CERT_IPV6_FILE "./cert_ipv6.pem"
+#define SERVER_CERT_SAN_TYPES_FILE "./cert_san_types.pem"
 #define SERVER_PRIVATE_KEY_FILE "./key.pem"
 #define CA_CERT_FILE "./ca-bundle.crt"
 #define CLIENT_CA_CERT_FILE "./rootCA.cert.pem"
@@ -14869,6 +14870,123 @@ TEST(SSLClientServerTest, TlsVerifyHostnameIpv6San) {
   EXPECT_FALSE(cn_ipv6_matched)
       << "An IPv6 host must not be authenticated via the certificate CN";
 }
+
+// A SAN entry must only match a host of its own type: the bytes of the dNSName
+// "a.zz" are also 97.46.122.122, and 42.46.122.122 reads as "*.zz".
+TEST(SSLClientServerTest, TlsVerifyHostnameSanType) {
+  using namespace httplib::tls;
+
+  // SANs: DNS:a.zz, IP:42.46.122.122
+  SSLServer svr(SERVER_CERT_SAN_TYPES_FILE, SERVER_PRIVATE_KEY_FILE);
+  ASSERT_TRUE(svr.is_valid());
+
+  svr.Get("/test", [](const Request &, Response &res) {
+    res.set_content("ok", "text/plain");
+  });
+
+  auto port = svr.bind_to_any_port(HOST);
+  thread t([&]() { svr.listen_after_bind(); });
+  auto se = detail::scope_exit([&] {
+    svr.stop();
+    t.join();
+  });
+  svr.wait_until_ready();
+
+  bool verify_callback_called = false;
+  bool dns_san_matched = false;
+  bool ip_san_matched = false;
+  bool ip_matched_via_dns_san = true;
+  bool dns_matched_via_ip_san = true;
+
+  SSLClient cli(HOST, port);
+  cli.enable_server_certificate_verification(true);
+  cli.set_ca_cert_path(CA_CERT_FILE);
+  cli.set_connection_timeout(5);
+
+  cli.set_server_certificate_verifier([&](const VerifyContext &ctx) -> bool {
+    verify_callback_called = true;
+    if (!ctx.cert) return false;
+
+    dns_san_matched = ctx.check_hostname("a.zz");
+    ip_san_matched = ctx.check_hostname("42.46.122.122");
+
+    ip_matched_via_dns_san = ctx.check_hostname("97.46.122.122");
+    dns_matched_via_ip_san = ctx.check_hostname("b.zz");
+
+    return true; // Accept for the purpose of this test
+  });
+
+  cli.Get("/test");
+
+  ASSERT_TRUE(verify_callback_called)
+      << "Verify callback should have been called";
+  EXPECT_TRUE(dns_san_matched) << "verify_hostname should match a dNSName SAN";
+  EXPECT_TRUE(ip_san_matched)
+      << "verify_hostname should match an iPAddress SAN";
+  EXPECT_FALSE(ip_matched_via_dns_san)
+      << "An IP host must not be authenticated via a dNSName SAN";
+  EXPECT_FALSE(dns_matched_via_ip_san)
+      << "A DNS host must not be authenticated via an iPAddress SAN";
+}
+
+// sans() must report each SAN entry under its own type.
+TEST(SSLClientServerTest, TlsCertSansEntryTypes) {
+  using namespace httplib::tls;
+
+  // SANs: DNS:a.zz, IP:42.46.122.122
+  SSLServer svr(SERVER_CERT_SAN_TYPES_FILE, SERVER_PRIVATE_KEY_FILE);
+  ASSERT_TRUE(svr.is_valid());
+
+  svr.Get("/test", [](const Request &, Response &res) {
+    res.set_content("ok", "text/plain");
+  });
+
+  auto port = svr.bind_to_any_port(HOST);
+  thread t([&]() { svr.listen_after_bind(); });
+  auto se = detail::scope_exit([&] {
+    svr.stop();
+    t.join();
+  });
+  svr.wait_until_ready();
+
+  bool verify_callback_called = false;
+  std::vector<SanEntry> sans;
+
+  SSLClient cli(HOST, port);
+  cli.enable_server_certificate_verification(true);
+  cli.set_ca_cert_path(CA_CERT_FILE);
+  cli.set_connection_timeout(5);
+
+  cli.set_server_certificate_verifier([&](const VerifyContext &ctx) -> bool {
+    verify_callback_called = true;
+    if (!ctx.cert) return false;
+
+    sans = ctx.sans();
+
+    return true; // Accept for the purpose of this test
+  });
+
+  cli.Get("/test");
+
+  ASSERT_TRUE(verify_callback_called)
+      << "Verify callback should have been called";
+
+  auto has_san = [&](SanType type, const std::string &value) {
+    return std::any_of(sans.begin(), sans.end(), [&](const SanEntry &san) {
+      return san.type == type && san.value == value;
+    });
+  };
+
+  EXPECT_TRUE(has_san(SanType::DNS, "a.zz"))
+      << "sans() should report the dNSName SAN";
+  EXPECT_TRUE(has_san(SanType::IP, "42.46.122.122"))
+      << "sans() should report the iPAddress SAN";
+
+  EXPECT_FALSE(has_san(SanType::IP, "97.46.122.122"))
+      << "sans() must not report the dNSName SAN as an address";
+  EXPECT_FALSE(has_san(SanType::DNS, "*.zz"))
+      << "sans() must not report the iPAddress SAN as a DNS name";
+}
 #endif
 
 // mbedTLS-specific callback constructor test