feat(go-sdk): add RA-TLS certificate verification package

[Leechael]

Summary

Add sdk/go/ratls package for RA-TLS (Remote Attestation TLS) certificate verification, enabling Go applications to verify that a TLS peer is running inside a genuine TDX TEE.

Verification chain (matches Rust ra-tls / dstack-attest)

1. Extract TDX quote from X.509 certificate extension (OID 1.3.6.1.4.1.62397.1.1)
2. Verify quote via dcap-qvl (fetch collateral from PCCS + verify Intel signature)
3. Validate TCB attributes — reject debug mode, check mr_signer_seam / mr_service_td are zero
4. Verify report_data binds to certificate public key — SHA512("ratls-cert:" || SubjectPublicKeyInfo DER)
5. Replay RTMR3 from event log (OID 1.3.6.1.4.1.62397.1.2) — filter event_type == 0x08000001, compute SHA384(event_type_le_bytes || ":" || event || ":" || payload), accumulate mr = SHA384(mr || digest)

API

// Verify a certificate extracted from a TLS connection
result, err := ratls.VerifyCert(cert, ratls.WithPCCSURL("https://pccs.phala.network"))

// Or use TLSConfig for automatic verification during TLS handshake
tlsCfg := ratls.TLSConfig(
    ratls.WithOnVerified(func(r *ratls.VerifyResult) {
        fmt.Println(r.Report.Status, r.Quote.Report.Type)
    }),
)
conn, err := tls.Dial("tcp", "endpoint:443", tlsCfg)

Module structure

sdk/go/ratls is a separate Go module (sdk/go/ratls/go.mod) to isolate the dcap-qvl CGO dependency from the base SDK module. This avoids pulling go-ethereum and other unrelated transitive dependencies into the base sdk/go/go.mod.

Consistency with Rust

Check	Rust source	Go implementation
Quote extraction	CertExt::get_extension_bytes() + yasna::parse_der	getExtensionBytes() + asn1.Unmarshal
DCAP verification	dcap_qvl::verify()	dcap.GetCollateralAndVerify()
TCB validation	validate_tcb() in dstack-attest	validateTCB()
report_data binding	QuoteContentType::RaTlsCert.to_report_data()	SHA512("ratls-cert:" || RawSubjectPublicKeyInfo)
RTMR3 replay	replay_runtime_events::<Sha384>()	verifyRTMR3()
Event digest	RuntimeEvent::digest::<Sha384>() with to_ne_bytes() (LE on x86_64)	binary.LittleEndian.PutUint32
Hex JSON decoding	serde_human_bytes	dcap.HexBytes

Test plan

• Run against a live RA-TLS endpoint:

  RATLS_TEST_ENDPOINT=host:port \
  CGO_LDFLAGS="-L/path/to/libdcap_qvl" \
  go test -v ./sdk/go/ratls/

• Verify consistency with Rust RA-TLS by comparing verification results on the same endpoint
• Demo integration: phala-cloud-gin-starter with go build -tags ratls