feat: backend service

gateway/authn/event.go

@@ -0,0 +1,80 @@
+package authn
+
+import (
+	"crypto/ed25519"
+	"encoding/binary"
+	"errors"
+)
+
+const (
+	// EventDomainMarkerV1 binds the v1 server event signature to the Galaxy
+	// gateway transport contract.
+	EventDomainMarkerV1 = "galaxy-event-v1"
+)
+
+var (
+	// ErrInvalidEventSignature reports that a gateway stream event signature is
+	// not a raw Ed25519 signature for the canonical event signing input.
+	ErrInvalidEventSignature = errors.New("invalid event signature")
+)
+
+// EventSigningFields contains the canonical v1 stream-event fields that are
+// bound into the server signing input.
+type EventSigningFields struct {
+	// EventType identifies the stable client-facing event category.
+	EventType string
+
+	// EventID is the stable event correlation identifier.
+	EventID string
+
+	// TimestampMS carries the server event timestamp in milliseconds.
+	TimestampMS int64
+
+	// RequestID optionally correlates the event to the opening client request.
+	RequestID string
+
+	// TraceID optionally carries the client-supplied tracing correlation value.
+	TraceID string
+
+	// PayloadHash is the raw SHA-256 digest of event payload bytes.
+	PayloadHash []byte
+}
+
+// BuildEventSigningInput returns the canonical byte sequence the v1 gateway
+// stream-event signature covers. String and byte fields are length-prefixed
+// with uvarint(len(field)) followed by raw bytes, while TimestampMS is
+// appended as an 8-byte big-endian uint64.
+func BuildEventSigningInput(fields EventSigningFields) []byte {
+	size := len(EventDomainMarkerV1) +
+		len(fields.EventType) +
+		len(fields.EventID) +
+		len(fields.RequestID) +
+		len(fields.TraceID) +
+		len(fields.PayloadHash) +
+		(6 * binary.MaxVarintLen64) +
+		8
+
+	buf := make([]byte, 0, size)
+	buf = appendLengthPrefixedString(buf, EventDomainMarkerV1)
+	buf = appendLengthPrefixedString(buf, fields.EventType)
+	buf = appendLengthPrefixedString(buf, fields.EventID)
+	buf = binary.BigEndian.AppendUint64(buf, uint64(fields.TimestampMS))
+	buf = appendLengthPrefixedString(buf, fields.RequestID)
+	buf = appendLengthPrefixedString(buf, fields.TraceID)
+	buf = appendLengthPrefixedBytes(buf, fields.PayloadHash)
+
+	return buf
+}
+
+// VerifyEventSignature verifies that signature authenticates fields under
+// publicKey using the canonical v1 event signing input.
+func VerifyEventSignature(publicKey ed25519.PublicKey, signature []byte, fields EventSigningFields) error {
+	if len(publicKey) != ed25519.PublicKeySize || len(signature) != ed25519.SignatureSize {
+		return ErrInvalidEventSignature
+	}
+	if !ed25519.Verify(publicKey, BuildEventSigningInput(fields), signature) {
+		return ErrInvalidEventSignature
+	}
+
+	return nil
+}