# Multi-Tenant Security Implementation Summary

## Overview

This document summarizes the Multi-Tenant Server Security features implemented for tenant isolation, cross-tenant access prevention, resource quotas, worker sanitization, and per-tenant audit logging.

---

## Tenant Isolation

### Tenant Manager (`internal/worker/tenant/manager.go`)

**Core Types:**
- `Tenant` - Represents an isolated tenant with metadata, config, and lifecycle state
- `TenantConfig` - Holds tenant-specific configuration including quotas and security policies
- `IsolationLevel` - Defines isolation degree: `soft`, `hard`, or `dedicated`

**Key Methods:**
- `CreateTenant()` - Creates isolated tenant workspace with subdirectories (artifacts, snapshots, logs, cache)
- `GetTenant()` - Retrieves active tenant by ID
- `DeactivateTenant()` - Soft-delete tenant
- `GetTenantWorkspace()` - Returns isolated workspace path for tenant
- `ListTenants()` - Returns all active tenants

**Workspace Isolation:**
```
/tenants/
  ├── {tenant-id}/
  │   ├── artifacts/
  │   ├── snapshots/
  │   ├── logs/
  │   └── cache/
```

**Security Defaults (`DefaultTenantConfig`):**
- IsolationLevel: `hard` (container-level)
- RequireEncryption: true
- RequireAuditLogging: true
- RequireSandbox: true
- NetworkPolicy: "restricted"

---

## Cross-Tenant Access Prevention

### Middleware (`internal/worker/tenant/middleware.go`)

**HTTP Middleware:**
- `Middleware.Handler()` - Validates tenant ID from headers/query params/context
- `ExtractTenantID()` - Extracts tenant ID from request (header: `X-Tenant-ID`, query param, or context)
- Automatic audit logging of all tenant requests

**Resource Access Control:**
- `ResourceAccessChecker` - Validates cross-tenant resource access
- `CheckAccess()` - Denies all cross-tenant access by default
- `CheckResourceOwnership()` - Validates resource belongs to requesting tenant
- `ValidateResourcePath()` - Ensures path within tenant workspace

**Cross-Tenant Denial:**
```go
// All cross-tenant access denied by default
if requestingTenantID != resourceTenantID {
    return fmt.Errorf("cross-tenant access denied")
}
```

---

## Resource Quotas per Tenant

### Quota Manager (`internal/worker/tenant/quota.go`)

**ResourceQuota Structure:**
- MaxConcurrentJobs - Job concurrency limit
- MaxGPUs - GPU allocation limit
- MaxMemoryGB - Memory usage limit
- MaxStorageGB - Storage quota
- MaxCPUCores - CPU core limit
- MaxRuntimeHours - Maximum job runtime
- MaxArtifactsPerHour - Artifact creation rate limit

**QuotaManager Features:**
- `CheckQuota()` - Validates resource request against tenant limits
- `Allocate()` - Reserves resources for tenant
- `Release()` - Frees resources when done
- `RecordArtifact()` - Tracks artifact creation rate
- Automatic hourly counter reset

**Default Quotas:**
```go
MaxConcurrentJobs:   5
MaxGPUs:             1
MaxMemoryGB:         32
MaxStorageGB:        100
MaxCPUCores:         8
MaxRuntimeHours:     24
MaxArtifactsPerHour: 10
```

---

## Worker Sanitization Between Tenants

### Sanitization (`internal/worker/tenant/manager.go`)

**SanitizeForTenant():**
- Clears tenant-specific caches
- Logs tenant transition for audit
- Prepares worker environment for different tenant

**Called When:**
- Worker switches between tenant tasks
- New tenant session begins

**Audit Event:** `AuditWorkerSanitized`

---

## Per-Tenant Audit Logging

### Audit Logger (`internal/worker/tenant/quota.go`)

**AuditEvent Types:**
- `AuditTenantCreated` - Tenant provisioned
- `AuditTenantDeactivated` - Tenant deactivated
- `AuditTenantUpdated` - Configuration changed
- `AuditResourceAccess` - Resource accessed
- `AuditResourceCreated` - Resource created
- `AuditResourceDeleted` - Resource deleted
- `AuditJobSubmitted` - Job queued
- `AuditJobCompleted` - Job finished
- `AuditJobFailed` - Job error
- `AuditCrossTenantDeny` - Cross-tenant blocked
- `AuditQuotaExceeded` - Quota violation
- `AuditWorkerSanitized` - Worker cleaned
- `AuditEncryptionOp` - Encryption operation
- `AuditDecryptionOp` - Decryption operation

**Audit Log Structure:**
```
/tenants/
  └── {tenant-id}/
      └── audit.log (JSON format)
```

**Features:**
- Per-tenant isolated log files
- Structured JSON format
- IP address tracking
- Success/failure status
- Detailed context in `Details` field

---

## Files Created

### Core Implementation
1. `internal/worker/tenant/manager.go` - Tenant lifecycle and isolation
2. `internal/worker/tenant/quota.go` - Resource quotas and audit logging
3. `internal/worker/tenant/middleware.go` - HTTP middleware and access control

### Worker Integration
4. `internal/worker/worker.go` - Added `TenantManager` field to Worker struct

---

## Testing

Build verification:
```bash
make dev  # Successful
```

All Go packages compile on:
- macOS (Darwin)
- Linux
- Windows

---

## Security Impact

| Feature | Threat Mitigated | Implementation |
|---------|------------------|----------------|
| Tenant Isolation | Data leakage between tenants | Hard isolation with dedicated workspaces |
| Cross-Tenant Access | Unauthorized data access | Deny-by-default with audit logging |
| Resource Quotas | Resource exhaustion / DoS | Per-tenant limits with enforcement |
| Worker Sanitization | Cross-contamination | State clearing between tenant switches |
| Per-Tenant Audit | Compliance gaps | Isolated audit logs per tenant |

---

## HIPAA Compliance

All features support HIPAA compliance:
- Tenant isolation ensures data separation
- Cross-tenant access prevention blocks unauthorized access
- Per-tenant audit logs enable compliance tracking
- Resource quotas prevent resource-based DoS

---

## Integration Points

**Worker Usage:**
```go
// Initialize tenant manager
w.TenantManager, _ = tenant.NewManager("/tenants", w.Logger)

// Create tenant
tenant, _ := w.TenantManager.CreateTenant(ctx, "tenant-1", "Acme Corp", config)

// Validate resource access
err := w.TenantManager.ValidateTenantAccess(ctx, requestingTenant, resourceTenant)

// Sanitize between tenants
w.TenantManager.SanitizeForTenant(ctx, newTenantID)
```

**HTTP Middleware Usage:**
```go
middleware := tenant.NewMiddleware(tenantManager, logger)
http.Handle("/api/", middleware.Handler(apiHandler))
```