fix(ssl): complete Apple TLS server and peer verification

[ithewei]

Summary

• load unencrypted RSA PKCS#1/PKCS#8 identities and PEM certificate chains for Apple TLS servers and mTLS clients
• explicitly verify peer chains, hostnames, system roots, and exclusive custom CA file/directory roots
• preserve libhv fd/event-loop ownership while fixing nonblocking handshake direction and containing Secure Transport deprecation warnings
• add strict bounded PEM/DER parsing, Apple TLS regression tests, deterministic fixtures, and Chinese TLS documentation

Compatibility

• public hssl API is unchanged
• local Apple identities require macOS 10.12+ or iOS 11.2+
• client-only Apple TLS remains availability-safe for older deployment targets
• EC and encrypted private keys remain unsupported by this backend

Verification

• make clean && ./configure && make libhv && make unittest
• bin/appletls_pem_test
• bin/appletls_test
• CMake shared/static library build
• strict Apple TLS compile with -Wall -Wextra -Werror
• iOS 9.0 and iOS 11.2 syntax/availability checks
• Clang static analyzer on ssl/appletls.c and ssl/appletls_pem.c
• bits-code-guard review: no unresolved P0-P2 findings

Notes

Network.framework was evaluated but cannot adopt libhv-owned connected file descriptors, so Secure Transport remains the compatibility backend and its deprecation warning is suppressed only inside ssl/appletls.c.

[Copilot]

Copilot review overview

🟡 Changes recommended

The documentation overstates cross-backend verification guarantees, and the new Apple-specific tests are not executed in CI.

Review effort: Balanced
Findings: 1 · 3

Open (4)

• macOS CI does not run the new Apple regression tests · New
• Backend-wide verification semantics do not match implementations · New
• GnuTLS verify_peer does not enforce client certificates · New
• CA directory behavior is incorrectly described as backend-independent · New

What changed in this PR

Completes Apple Secure Transport support for identities, peer verification, nonblocking handshakes, and regression coverage.

Changes:

• Adds bounded PEM/DER parsing and Apple TLS identity/trust handling.
• Adds Apple TLS handshake, mTLS, hostname, and parser tests with fixtures.
• Improves SNI failure handling and adds Chinese TLS documentation.

File	Description
ssl/​appletls.c	Implements Apple identities, verification, and handshake fixes.
ssl/​appletls_pem.c	Adds bounded PEM/DER parsing.
ssl/​appletls_pem.h	Declares internal parser API and limits.
event/​tls.c	Handles SNI setup failures.
http/​client/​HttpClient.cpp	Propagates synchronous SNI setup failures.
Makefile	Builds Apple TLS tests on Darwin.
scripts/​unittest.sh	Conditionally runs Apple TLS tests.
unittest/​appletls_test.c	Tests handshakes, verification, and mTLS.
unittest/​appletls_pem_test.c	Tests parser formats and limits.
unittest/​fixtures/​appletls/​generate.sh	Regenerates TLS fixtures.
unittest/​fixtures/​appletls/​README.md	Documents fixture usage.
unittest/​fixtures/​appletls/​root.crt	Test root CA.
unittest/​fixtures/​appletls/​root.der	DER root CA fixture.
unittest/​fixtures/​appletls/​intermediate.crt	Intermediate CA fixture.
unittest/​fixtures/​appletls/​server.crt	Server certificate fixture.
unittest/​fixtures/​appletls/​server-chain.pem	Server certificate chain.
unittest/​fixtures/​appletls/​server-pkcs1.key	PKCS#1 server key.
unittest/​fixtures/​appletls/​server-pkcs8.key	PKCS#8 server key.
unittest/​fixtures/​appletls/​client.crt	mTLS client certificate.
unittest/​fixtures/​appletls/​client.key	mTLS client key.
unittest/​fixtures/​appletls/​client-chain.pem	Client certificate chain.
unittest/​fixtures/​appletls/​wrong-root.crt	Untrusted CA fixture.
unittest/​fixtures/​appletls/​wrong-server.key	Mismatched key fixture.
unittest/​fixtures/​appletls/​multi-ca.pem	Multiple-CA fixture.
unittest/​fixtures/​appletls/​ec-sec1.key	Unsupported SEC1 EC key.
unittest/​fixtures/​appletls/​ec-pkcs8.key	Unsupported PKCS#8 EC key.
unittest/​fixtures/​appletls/​encrypted-key.pem	Unsupported encrypted key.
unittest/​fixtures/​appletls/​malformed-base64.pem	Invalid Base64 fixture.
unittest/​fixtures/​appletls/​malformed-pkcs8.pem	Invalid PKCS#8 fixture.
unittest/​fixtures/​appletls/​ca-dir/​root.crt	CA-directory certificate.
unittest/​fixtures/​appletls/​ca-dir/​README.txt	Non-certificate directory noise.
unittest/​fixtures/​appletls/​empty-ca-dir/​README.txt	Empty CA-source fixture.
docs/​cn/​TcpServer.md	Documents server TLS and mTLS.
docs/​cn/​TcpClient.md	Documents client verification and mTLS.

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[Copilot]

Copilot review overview

🟡 Changes recommended

Optional client-certificate requests incorrectly abort, and Apple tests fail to link when another TLS backend is configured on macOS.

Review effort: Balanced
Findings: 1

Open (1)

• Enable Apple TLS backend in backend-specific test target · New

Resolved since last review (4)

• macOS CI does not run the new Apple regression tests
• CA directory behavior is incorrectly described as backend-independent
• GnuTLS verify_peer does not enforce client certificates
• Backend-wide verification semantics do not match implementations

Previously missed (1)

In code that hasn't changed since last review

Allow session resumption without optional client certificate

ssl/​appletls.c:1287

This makes a client without a local identity abort whenever a server merely requests an optional client certificate. A client is allowed to resume without sending one; a server configured to require mTLS will then reject it itself. The previous implementation resumed here, and retaining that behavior preserves connections to servers using optional client authentication.