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Tim Bendt d359baa010 Add conflict resolution diff UI and app branding

2026-05-13 16:25:28 -04:00

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Security Specification

Threat Model

Assets

Document Content: Markdown files and attachments
User Credentials: Passkeys, passwords, session tokens
Collaboration Data: Comments, notifications, history
System State: Database, configuration, logs

Threat Actors

External Attacker: No system access, attempts remote exploitation
Malicious User: Authenticated, attempts unauthorized access
Compromised Client: Legitimate user's device infected
Insider: Administrator or developer with system access

Threats

Supply Chain Attack: Malicious dependency injection
Authentication Bypass: Session hijacking, credential theft
Authorization Bypass: Horizontal/vertical privilege escalation
Data Exfiltration: Unauthorized document access
Data Tampering: Modification without authorization
Denial of Service: Resource exhaustion
Information Disclosure: Secrets in logs/responses

Security Controls

1. Supply Chain Security

Policy:

Only dependencies with >1M downloads/month or official Go team
All versions pinned in go.sum
No transitive dependencies without review
Prefer standard library when possible

Implementation:

# go.mod
require (
    github.com/go-chi/chi/v5 v5.0.12
    github.com/tursodatabase/libsql-client-go v0.0.0-20240416075031-555ce55511f7
    // All versions pinned
)

# Build
RUN go mod verify  # Verify checksums
RUN go mod vendor  # Optional: vendor for air-gapped

Audit:

Weekly govulncheck scan
Dependency review in CI
No build-time network access (vendored or proxy with checksum)

2. Authentication Security

Passkey (WebAuthn)

// Registration
func registerPasskey(user User) (*Credential, error) {
    options, session, err := webauthn.BeginRegistration(user)
    // Store session data server-side (never client-side)
    // Return options to client
}

func verifyRegistration(sessionID string, response ProtocolCredentialCreation) (*Credential, error) {
    session := getSessionData(sessionID)
    credential, err := webauthn.FinishRegistration(user, session, response)
    // Verify attestation
    // Store credential: ID, public key, sign count
}

Password (Argon2id)

import "golang.org/x/crypto/argon2"

const (
    timeCost    = 3
    memoryCost  = 64 * 1024  // 64MB
    parallelism = 4
    saltLength  = 16
    keyLength   = 32
)

func hashPassword(password string) (string, error) {
    salt := make([]byte, saltLength)
    if _, err := rand.Read(salt); err != nil {
        return "", err
    }
    
    hash := argon2.IDKey([]byte(password), salt, timeCost, memoryCost, parallelism, keyLength)
    
    // Encode to string: $argon2id$v=19$m=65536,t=3,p=4$<salt>$<hash>
    return encodeHash(salt, hash), nil
}

func verifyPassword(password, encodedHash string) (bool, error) {
    salt, hash, params, err := decodeHash(encodedHash)
    if err != nil {
        return false, err
    }
    
    computedHash := argon2.IDKey([]byte(password), salt, params.time, params.memory, params.parallelism, uint32(len(hash)))
    
    // Constant-time comparison
    return subtle.ConstantTimeCompare(hash, computedHash) == 1, nil
}

Session Management

func createSession(userID string, r *http.Request) (*Session, error) {
    token := make([]byte, 32)
    if _, err := rand.Read(token); err != nil {
        return nil, err
    }
    
    session := &Session{
        ID:        uuid.New().String(),
        UserID:    userID,
        TokenHash: sha256.Sum256(token),
        CreatedAt: time.Now(),
        ExpiresAt: time.Now().Add(24 * time.Hour),
        IP:        r.RemoteAddr,
        UserAgent: r.UserAgent(),
    }
    
    // Store in database
    if err := db.CreateSession(session); err != nil {
        return nil, err
    }
    
    // Set cookie
    http.SetCookie(w, &http.Cookie{
        Name:     "session",
        Value:    base64.URLEncoding.EncodeToString(token),
        Expires:  session.ExpiresAt,
        HttpOnly: true,
        Secure:   true,        // HTTPS only
        SameSite: http.SameSiteStrictMode,
        Path:     "/",
    })
    
    return session, nil
}

3. Authorization

Permission Model

type Permission string

const (
    PermissionRead  Permission = "read"
    PermissionWrite Permission = "write"
    PermissionAdmin Permission = "admin"
)

type ResourceType string

const (
    ResourceGlobal     ResourceType = "global"
    ResourceCollection ResourceType = "collection"
    ResourceDocument   ResourceType = "document"
)

func checkPermission(userID string, resourceType ResourceType, resourceID string, required Permission) (bool, error) {
    // Check explicit permission
    perm, err := db.GetPermission(userID, resourceType, resourceID)
    if err == nil && hasPermission(perm.Permission, required) {
        return true, nil
    }
    
    // Check collection permission for documents
    if resourceType == ResourceDocument {
        collectionID := getDocumentCollection(resourceID)
        perm, err = db.GetPermission(userID, ResourceCollection, collectionID)
        if err == nil && hasPermission(perm.Permission, required) {
            return true, nil
        }
    }
    
    // Check global permission
    perm, err = db.GetPermission(userID, ResourceGlobal, "")
    if err == nil && hasPermission(perm.Permission, required) {
        return true, nil
    }
    
    // Check document public status
    if resourceType == ResourceDocument && required == PermissionRead {
        doc, err := db.GetDocument(resourceID)
        if err == nil && doc.PublicRead {
            return true, nil
        }
    }
    
    return false, nil
}

Middleware

func RequirePermission(resourceType ResourceType, required Permission) func(http.Handler) http.Handler {
    return func(next http.Handler) http.Handler {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            userID := getUserID(r.Context())
            resourceID := chi.URLParam(r, "id")
            
            allowed, err := checkPermission(userID, resourceType, resourceID, required)
            if err != nil || !allowed {
                http.Error(w, "Forbidden", http.StatusForbidden)
                return
            }
            
            next.ServeHTTP(w, r)
        })
    }
}

// Usage:
r.With(RequirePermission(ResourceDocument, PermissionRead)).
    Get("/docs/{id}", getDocumentHandler)

4. Input Validation

Markdown Sanitization

import "github.com/yuin/goldmark"
import "github.com/yuin/goldmark/extension"
import "github.com/yuin/goldmark/renderer/html"

func renderMarkdown(source []byte) ([]byte, error) {
    md := goldmark.New(
        goldmark.WithExtensions(
            extension.Table,
            extension.Strikethrough,
            extension.Linkify,
            // No raw HTML extension — we control HTML output
        ),
        goldmark.WithRendererOptions(
            html.WithHardWraps(),
            html.WithXHTML(),
            html.WithUnsafe(), // DISABLED — no raw HTML passthrough
        ),
    )
    
    var buf bytes.Buffer
    if err := md.Convert(source, &buf); err != nil {
        return nil, err
    }
    
    return buf.Bytes(), nil
}

File Upload Validation

func validateUpload(file io.Reader, filename string, maxSize int64) ([]byte, string, error) {
    // Size limit
    limited := io.LimitReader(file, maxSize+1)
    data, err := io.ReadAll(limited)
    if err != nil {
        return nil, "", err
    }
    if int64(len(data)) > maxSize {
        return nil, "", fmt.Errorf("file too large")
    }
    
    // Magic number validation
    contentType := detectContentType(data)
    allowedTypes := map[string]bool{
        "image/jpeg": true,
        "image/png": true,
        "image/gif": true,
        "image/webp": true,
        "application/pdf": true,
    }
    if !allowedTypes[contentType] {
        return nil, "", fmt.Errorf("file type not allowed")
    }
    
    // Extension whitelist
    ext := strings.ToLower(filepath.Ext(filename))
    allowedExts := map[string]bool{
        ".jpg": true, ".jpeg": true, ".png": true,
        ".gif": true, ".webp": true, ".pdf": true,
    }
    if !allowedExts[ext] {
        return nil, "", fmt.Errorf("file extension not allowed")
    }
    
    // Compute hash
    hash := sha256.Sum256(data)
    hashStr := hex.EncodeToString(hash[:])
    
    return data, hashStr, nil
}

Path Sanitization

func sanitizePath(userPath string) (string, error) {
    // Clean the path
    clean := filepath.Clean(userPath)
    
    // Prevent traversal
    if strings.Contains(clean, "..") {
        return "", fmt.Errorf("path traversal detected")
    }
    
    // Ensure it's relative
    if filepath.IsAbs(clean) {
        return "", fmt.Errorf("absolute paths not allowed")
    }
    
    // Join with base and verify it's within base
    fullPath := filepath.Join(baseDir, clean)
    if !strings.HasPrefix(filepath.Clean(fullPath), filepath.Clean(baseDir)) {
        return "", fmt.Errorf("path outside allowed directory")
    }
    
    return clean, nil
}

5. Transport Security

TLS Configuration

tlsConfig := &tls.Config{
    MinVersion: tls.VersionTLS13,
    CurvePreferences: []tls.CurveID{
        tls.X25519,
        tls.CurveP256,
    },
    CipherSuites: []uint16{
        tls.TLS_AES_256_GCM_SHA384,
        tls.TLS_CHACHA20_POLY1305_SHA256,
        tls.TLS_AES_128_GCM_SHA256,
    },
    PreferServerCipherSuites: true,
}

Security Headers

func securityHeaders(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Security-Policy",
            "default-src 'self'; "+
            "script-src 'self' 'nonce-{nonce}'; "+
            "style-src 'self' 'unsafe-inline'; "+
            "img-src 'self' data:; "+
            "connect-src 'self' wss:; "+
            "frame-ancestors 'none'; "+
            "base-uri 'self'; "+
            "form-action 'self';")
        w.Header().Set("X-Content-Type-Options", "nosniff")
        w.Header().Set("X-Frame-Options", "DENY")
        w.Header().Set("X-XSS-Protection", "1; mode=block")
        w.Header().Set("Referrer-Policy", "strict-origin-when-cross-origin")
        w.Header().Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains; preload")
        w.Header().Set("Permissions-Policy", "camera=(), microphone=(), geolocation=()")
        
        next.ServeHTTP(w, r)
    })
}

6. Operational Security

Logging

func logAudit(event AuditEvent) {
    entry := slog.With(
        "event_type", event.Type,
        "actor_id", redactIfSecret(event.ActorID),
        "resource_type", event.ResourceType,
        "resource_id", redactIfSecret(event.ResourceID),
        "ip", event.IP,
        "timestamp", event.Timestamp,
    )
    
    // Never log: passwords, tokens, session IDs, API keys
    entry.Info("audit event")
}

func redactIfSecret(value string) string {
    if looksLikeSecret(value) {
        return "[REDACTED]"
    }
    return value
}

Container Security

# Dockerfile
FROM golang:1.22-alpine AS builder
# ... build ...

FROM alpine:3.19
RUN addgroup -g 1000 appgroup && \
    adduser -u 1000 -G appgroup -s /bin/sh -D appuser

# Read-only root filesystem
COPY --from=builder /app/server /server
COPY --from=builder /app/web/dist /web

# Data directory (writable)
RUN mkdir /data && chown appuser:appgroup /data
VOLUME /data

USER appuser
EXPOSE 8080

HEALTHCHECK --interval=30s --timeout=3s \
    CMD wget -q --spider http://localhost:8080/health || exit 1

ENTRYPOINT ["/server"]

Incident Response

Detection

Automated alerts on: failed auth spikes, permission errors, large file uploads
Log analysis for anomalies
Health check failures

Response

Isolate: Block IP, revoke sessions, disable account if compromised
Assess: Determine scope of breach, affected data
Contain: Patch vulnerability, rotate secrets
Recover: Restore from clean backup if necessary
Document: Post-incident review, update security measures

Compliance

Data minimization: only email stored, no other PII
Right to erasure: /api/user/delete endpoint
Data portability: /api/user/export endpoint
Consent: explicit opt-in for email notifications

Audit Trail

All security-relevant events logged:

Authentication attempts (success/failure)
Permission changes
Document access (if private)
Admin actions
Configuration changes

Retention: 90 days active, 1 year archive

12 KiB Raw Blame History

Security Specification

Threat Model

Assets

Threat Actors

Threats

Security Controls

1. Supply Chain Security

2. Authentication Security

Passkey (WebAuthn)

Password (Argon2id)

Session Management

3. Authorization

Permission Model

Middleware

4. Input Validation

Markdown Sanitization

File Upload Validation

Path Sanitization

5. Transport Security

TLS Configuration

Security Headers

6. Operational Security

Logging

Container Security

Incident Response

Detection

Response

Compliance

GDPR

Audit Trail

12 KiB

Raw Blame History