feat(sense): implement Control API v1 [T-011]

Sense/internal/auth/auth.go

@@ -0,0 +1,181 @@
+// Package auth defines the verified principal boundary for Sense HTTP APIs.
+package auth
+
+import (
+	"context"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strings"
+)
+
+const (
+	PermissionDevicesRead  = "sense.devices.read"
+	PermissionDevicesWrite = "sense.devices.write"
+)
+
+var (
+	ErrUnauthenticated = errors.New("unauthenticated")
+	logicalIDPattern   = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._:-]{0,63}$`)
+)
+
+type Principal struct {
+	SubjectID   string
+	ActorType   string
+	TenantID    string
+	SiteIDs     []string
+	Permissions map[string]struct{}
+}
+
+func (p Principal) AllowsSite(siteID string) bool {
+	for _, allowed := range p.SiteIDs {
+		if allowed == "*" || allowed == siteID {
+			return true
+		}
+	}
+	return false
+}
+
+func (p Principal) Has(permission string) bool {
+	_, ok := p.Permissions[permission]
+	return ok
+}
+
+type Authenticator interface {
+	Authenticate(context.Context, string) (Principal, error)
+}
+
+type staticFile struct {
+	Version    int               `json:"version"`
+	Principals []staticPrincipal `json:"principals"`
+}
+
+type staticPrincipal struct {
+	TokenSHA256 string   `json:"token_sha256"`
+	SubjectID   string   `json:"subject_id"`
+	ActorType   string   `json:"actor_type"`
+	TenantID    string   `json:"tenant_id"`
+	SiteIDs     []string `json:"site_ids"`
+	Permissions []string `json:"permissions"`
+}
+
+type staticEntry struct {
+	digest    [sha256.Size]byte
+	principal Principal
+}
+
+// StaticSHA256 authenticates opaque tokens against externally provisioned
+// SHA-256 digests. The source file is read only during process startup.
+type StaticSHA256 struct {
+	entries []staticEntry
+}
+
+func LoadStaticSHA256(path string) (*StaticSHA256, error) {
+	contents, err := os.ReadFile(path)
+	if err != nil {
+		return nil, errors.New("read static authentication registry")
+	}
+	decoder := json.NewDecoder(strings.NewReader(string(contents)))
+	decoder.DisallowUnknownFields()
+	var document staticFile
+	if err := decoder.Decode(&document); err != nil {
+		return nil, errors.New("decode static authentication registry")
+	}
+	if err := decoder.Decode(&struct{}{}); err != io.EOF {
+		return nil, errors.New("static authentication registry has trailing JSON")
+	}
+	if document.Version != 1 || len(document.Principals) == 0 {
+		return nil, errors.New("static authentication registry must contain version 1 principals")
+	}
+	entries := make([]staticEntry, 0, len(document.Principals))
+	seenDigests := make(map[string]struct{}, len(document.Principals))
+	for index, value := range document.Principals {
+		entry, validationErr := parseStaticPrincipal(value)
+		if validationErr != nil {
+			return nil, fmt.Errorf("invalid static authentication principal %d: %w", index, validationErr)
+		}
+		if _, exists := seenDigests[value.TokenSHA256]; exists {
+			return nil, errors.New("duplicate static authentication token digest")
+		}
+		seenDigests[value.TokenSHA256] = struct{}{}
+		entries = append(entries, entry)
+	}
+	return &StaticSHA256{entries: entries}, nil
+}
+
+func parseStaticPrincipal(value staticPrincipal) (staticEntry, error) {
+	var entry staticEntry
+	if len(value.TokenSHA256) != sha256.Size*2 || value.TokenSHA256 != strings.ToLower(value.TokenSHA256) {
+		return entry, errors.New("token_sha256 must be 64 lowercase hexadecimal characters")
+	}
+	digest, err := hex.DecodeString(value.TokenSHA256)
+	if err != nil {
+		return entry, errors.New("token_sha256 must be hexadecimal")
+	}
+	copy(entry.digest[:], digest)
+	if strings.TrimSpace(value.SubjectID) == "" || len(value.SubjectID) > 200 {
+		return entry, errors.New("subject_id must contain 1 to 200 characters")
+	}
+	if value.ActorType != "user" && value.ActorType != "service" {
+		return entry, errors.New("actor_type must be user or service")
+	}
+	if !logicalIDPattern.MatchString(value.TenantID) {
+		return entry, errors.New("tenant_id is invalid")
+	}
+	if len(value.SiteIDs) == 0 {
+		return entry, errors.New("site_ids must not be empty")
+	}
+	sites := make([]string, 0, len(value.SiteIDs))
+	seenSites := make(map[string]struct{}, len(value.SiteIDs))
+	for _, siteID := range value.SiteIDs {
+		if siteID != "*" && !logicalIDPattern.MatchString(siteID) {
+			return entry, errors.New("site_ids contains an invalid site")
+		}
+		if _, exists := seenSites[siteID]; exists {
+			return entry, errors.New("site_ids contains a duplicate")
+		}
+		seenSites[siteID] = struct{}{}
+		sites = append(sites, siteID)
+	}
+	permissions := make(map[string]struct{}, len(value.Permissions))
+	for _, permission := range value.Permissions {
+		if permission != PermissionDevicesRead && permission != PermissionDevicesWrite {
+			return entry, errors.New("permissions contains an unsupported value")
+		}
+		if _, exists := permissions[permission]; exists {
+			return entry, errors.New("permissions contains a duplicate")
+		}
+		permissions[permission] = struct{}{}
+	}
+	if len(permissions) == 0 {
+		return entry, errors.New("permissions must not be empty")
+	}
+	entry.principal = Principal{
+		SubjectID: value.SubjectID, ActorType: value.ActorType, TenantID: value.TenantID,
+		SiteIDs: sites, Permissions: permissions,
+	}
+	return entry, nil
+}
+
+func (a *StaticSHA256) Authenticate(_ context.Context, token string) (Principal, error) {
+	if len(token) < 22 || len(token) > 4096 {
+		return Principal{}, ErrUnauthenticated
+	}
+	digest := sha256.Sum256([]byte(token))
+	match := -1
+	for index := range a.entries {
+		if subtle.ConstantTimeCompare(digest[:], a.entries[index].digest[:]) == 1 {
+			match = index
+		}
+	}
+	if match < 0 {
+		return Principal{}, ErrUnauthenticated
+	}
+	return a.entries[match].principal, nil
+}