Add native API for TLS 1.3 certificate_authorities extension

[julek-wolfssl]

RFC 8446 4.2.4 certificate_authorities (extension type 47) was previously only accessible behind OPENSSL_EXTRA via the client_ca_names / ca_names / peer_ca_names WOLF_STACK_OF(WOLFSSL_X509_NAME) stacks, leaving users without the OpenSSL compat layer no way to send or inspect the extension. This adds a native API gated on WOLFSSL_TLS13.

• New CertificateAuthority node type: a singly-linked list with a flexible-array DN buffer holding the inner DER-encoded Name content (no SEQUENCE header). TLSX_CertificateAuthorities_Add/FreeAll manage the list, gated on WOLFSSL_TLS13 && !NO_CERTS && !WOLFSSL_NO_CA_NAMES.

• Storage added on WOLFSSL_CTX (ws_ca_names) and WOLFSSL (ws_ca_names + ws_peer_ca_names); SSL shadows CTX via the WS_CA_NAMES helper.

• New public API mirroring the UseSNI style:

  • wolfSSL_UseCertificateAuthority / CTX variant
  • wolfSSL_ClearCertificateAuthorities / CTX variant
  • wolfSSL_GetPeerCertificateAuthorityCount
  • wolfSSL_GetPeerCertificateAuthority (index-based, copy-out)

  The library prepends the DER SEQUENCE header on the wire and strips it on parse, so callers pass the raw subject content straight from wc_GetDecodedCertSubjectRaw (new accessor on DecodedCert).

• TLSX_CA_Names_Write is a single emitter matching the PHA_GET_SIZE / PHA_WRITE style (int return, word16* pSz accumulator); macros pass NULL when sizing and the output buffer when serializing. It walks the compat stack first (when OPENSSL_EXTRA is on) then the native list, enforcing the RFC 8446 per-DN cap and capping the whole extension payload (outer length included) at WOLFSSL_MAX_16BIT so the word16 size accumulator stays exact, returning BUFFER_ERROR on overflow.

• TLSX_CA_Names_Parse always populates ws_peer_ca_names and, when OPENSSL_EXTRA is compiled in, additionally populates peer_ca_names through the existing InitDecodedCert/GetName/CopyDecodedName path. Length validation enforces the RFC 8446 DistinguishedName<1..2^16-1> and authorities<3..2^16-1> bounds.

• TLSX_GetSize now propagates a non-zero ret by breaking out of the walk, matching TLSX_Write.

• Teardown paths in SSL_CtxResourceFree and wolfSSL_ResourceFree free the native lists on the owning heap.

Tests added in tests/api/test_tls_ext.c cover argument validation, size limits, send/receive counts, handshake round-trips on SSL and CTX, a cert_cb scenario feeding DecodedCert subjects to the API (with a params loop for TLS 1.3 and DTLS 1.3), the existing OPENSSL_EXTRA cases, and a bad-extension regression. Documentation for all new API functions is added under doc/dox_comments/header_files/.

[Copilot]

Pull request overview

This PR adds a wolfSSL-native API (gated on WOLFSSL_TLS13) for sending and inspecting the TLS 1.3 certificate_authorities extension (RFC 8446 §4.2.4), making the feature available without requiring the OpenSSL compatibility layer.

Changes:

• Introduces a native CertificateAuthority linked-list representation, stored on WOLFSSL_CTX / WOLFSSL, with emit/parse support integrated into TLS extensions.
• Adds public APIs to configure advertised CA DNs and to query peer-provided CA DNs, plus a new wc_GetDecodedCertSubjectRaw() accessor to supply correctly-formatted DN content.
• Adds API tests covering argument validation, size limits, handshake round-trips (SSL + CTX), and a cert_cb scenario.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
wolfssl/wolfcrypt/asn_public.h	Declares new public accessor for raw subject DN content (wc_GetDecodedCertSubjectRaw).
wolfcrypt/src/asn.c	Implements wc_GetDecodedCertSubjectRaw() returning the inner subject Name SEQUENCE content pointer/length.
wolfssl/ssl.h	Adds the new public native certificate_authorities API declarations and header-level documentation.
wolfssl/internal.h	Adds native CA list node type and storage fields in WOLFSSL_CTX/WOLFSSL, plus helper macro for CTX fallback.
src/tls.c	Implements native CA list management and unified extension sizing/writing/parsing for compat + native sources.
src/ssl_api_ext.c	Implements the new public native APIs (Use/Clear/GetPeerCount/GetPeerByIndex).
src/ssl_api_cert.c	Tightens OpenSSL-compat CA-names code compilation guards to OPENSSL_EXTRA.
src/internal.c	Adds teardown of native lists and adjusts CA-names-related guards in resource free paths.
tests/api/test_tls_ext.h	Adds prototypes for new native API tests.
tests/api/test_tls_ext.c	Adds comprehensive native API tests, including handshake and cert-callback coverage.
tests/api.c	Registers new tests in the main API test list.
doc/dox_comments/header_files/ssl.h	Adds doxygen documentation for the new SSL/CTX APIs and peer getters.
doc/dox_comments/header_files/asn_public.h	Adds doxygen documentation for wc_GetDecodedCertSubjectRaw().

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated no new comments.

Suppressed comments (3)

doc/dox_comments/header_files/asn_public.h:4417

• The lifetime/ownership statement is incorrect: subjectRaw points into the source DER buffer passed to wc_InitDecodedCert, which DecodedCert does not own. A caller can keep the DecodedCert alive but free/reuse that source buffer and then dereference a dangling pointer. Document that the source DER must remain alive while the returned pointer is used.

    The returned pointer and size reference the inner content of the subject
    Name SEQUENCE (i.e. the bytes after the SEQUENCE tag and length). The
    pointer aliases memory inside the DecodedCert and must not be freed by
    the caller. The data remains valid until the DecodedCert is freed.

wolfcrypt/src/asn.c:23312

• cert->subjectRaw aliases cert->source, and InitDecodedCert explicitly does not own that source buffer. This comment currently gives the opposite ownership impression and could lead future callers to rely only on the DecodedCert lifetime. State that the input DER buffer controls this pointer's lifetime.
  src/tls.c:7864
• This still accepts an empty authorities vector (00 00). RFC 8446 defines authorities<3..2^16-1>, so an extension that is present must contain at least three vector bytes; accepting zero bypasses the stated malformed-extension validation. Reject every post-prefix length below 3.

    if (length > 0 && length < 3)