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+# Authentication Dependencies Guide
+
+## Overview
+
+FastAPI routes use different authentication dependencies based on whether they serve **HTML pages** or **API endpoints**.
+
+## Available Dependencies
+
+### Admin Authentication
+
+| Dependency | Use Case | Accepts | Description |
+|------------|----------|---------|-------------|
+| `get_current_admin_from_cookie_or_header` | HTML pages | Cookie OR Header | For admin HTML routes like `/admin/dashboard` |
+| `get_current_admin_api` | API endpoints | Header ONLY | For admin API routes like `/api/v1/admin/vendors` |
+| `get_current_admin_optional` | Login pages | Cookie OR Header | Returns `None` instead of raising exception |
+
+### Vendor Authentication
+
+| Dependency | Use Case | Accepts | Description |
+|------------|----------|---------|-------------|
+| `get_current_vendor_from_cookie_or_header` | HTML pages | Cookie OR Header | For vendor HTML routes like `/vendor/{code}/dashboard` |
+| `get_current_vendor_api` | API endpoints | Header ONLY | For vendor API routes like `/api/v1/vendor/{code}/products` |
+| `get_current_vendor_optional` | Login pages | Cookie OR Header | Returns `None` instead of raising exception |
+
+### Customer Authentication
+
+| Dependency | Use Case | Accepts | Description |
+|------------|----------|---------|-------------|
+| `get_current_customer_from_cookie_or_header` | HTML pages | Cookie OR Header | For shop account pages like `/shop/account/dashboard` |
+| `get_current_customer_api` | API endpoints | Header ONLY | For shop API routes like `/api/v1/shop/cart` |
+| `get_current_customer_optional` | Login pages | Cookie OR Header | Returns `None` instead of raising exception |
+
+## When to Use Which?
+
+### Use `_from_cookie_or_header` for HTML Pages
+
+HTML pages that render templates and are accessed by browsers:
+
+```python
+# app/routes/admin_pages.py
+from app.api.deps import get_current_admin_from_cookie_or_header
+
+@router.get("/admin/dashboard", response_class=HTMLResponse)
+async def admin_dashboard(
+    request: Request,
+    current_user: User = Depends(get_current_admin_from_cookie_or_header)
+):
+    return templates.TemplateResponse("admin/dashboard.html", {...})
+```
+
+**Why?** Browsers automatically send cookies, making this seamless for page navigation.
+
+### Use `_api` for API Endpoints
+
+JSON API endpoints that are called by JavaScript:
+
+```python
+# app/api/v1/admin/vendors.py
+from app.api.deps import get_current_admin_api
+
+@router.get("/api/v1/admin/vendors")
+async def list_vendors(
+    current_user: User = Depends(get_current_admin_api),
+    db: Session = Depends(get_db)
+):
+    return {"vendors": [...]}
+```
+
+**Why?**
+- **Security**: API endpoints should NOT accept cookies (prevents CSRF attacks)
+- **Explicit**: JavaScript must explicitly set Authorization header
+- **Stateless**: API calls are stateless and don't rely on browser cookies
+
+### Use `_optional` for Login Pages
+
+Login pages that redirect if already authenticated:
+
+```python
+# app/routes/admin_pages.py
+from app.api.deps import get_current_admin_optional
+
+@router.get("/admin/login", response_class=HTMLResponse)
+async def admin_login_page(
+    request: Request,
+    current_user: Optional[User] = Depends(get_current_admin_optional)
+):
+    if current_user:
+        return RedirectResponse("/admin/dashboard")
+    return templates.TemplateResponse("admin/login.html", {...})
+```
+
+**Why?** Avoids showing login page to already-authenticated users.
+
+## Migration Guide
+
+### Old vs New Names
+
+The authentication dependencies were renamed for clarity:
+
+| ❌ Old Name (REMOVED) | ✅ New Name | Type |
+|----------------------|-------------|------|
+| `get_current_admin_user` | `get_current_admin_from_cookie_or_header` | HTML pages |
+| `get_current_admin_user` | `get_current_admin_api` | API endpoints |
+| `get_current_vendor_user` | `get_current_vendor_from_cookie_or_header` | HTML pages |
+| `get_current_vendor_user` | `get_current_vendor_api` | API endpoints |
+
+### How to Update Your Code
+
+1. **Identify route type**: Is it an HTML page or API endpoint?
+2. **Choose correct dependency**:
+   - HTML page → `_from_cookie_or_header`
+   - API endpoint → `_api`
+3. **Update import and usage**
+
+#### Example 1: HTML Page Route
+
+**Before:**
+```python
+from app.api.deps import get_current_admin_user  # ❌ Doesn't exist
+
+@router.get("/admin/settings")
+def settings_page(current_user: User = Depends(get_current_admin_user)):
+    ...
+```
+
+**After:**
+```python
+from app.api.deps import get_current_admin_from_cookie_or_header  # ✅
+
+@router.get("/admin/settings")
+def settings_page(
+    current_user: User = Depends(get_current_admin_from_cookie_or_header)
+):
+    ...
+```
+
+#### Example 2: API Endpoint
+
+**Before:**
+```python
+from app.api.deps import get_current_admin_user  # ❌ Doesn't exist
+
+@router.post("/api/v1/admin/vendors")
+def create_vendor(current_user: User = Depends(get_current_admin_user)):
+    ...
+```
+
+**After:**
+```python
+from app.api.deps import get_current_admin_api  # ✅
+
+@router.post("/api/v1/admin/vendors")
+def create_vendor(current_user: User = Depends(get_current_admin_api)):
+    ...
+```
+
+## Quick Reference
+
+```python
+# All available in app.api.deps
+
+# ADMIN
+from app.api.deps import (
+    get_current_admin_from_cookie_or_header,  # HTML pages
+    get_current_admin_api,                     # API endpoints
+    get_current_admin_optional,                # Login pages
+)
+
+# VENDOR
+from app.api.deps import (
+    get_current_vendor_from_cookie_or_header,  # HTML pages
+    get_current_vendor_api,                     # API endpoints
+    get_current_vendor_optional,                # Login pages
+)
+
+# CUSTOMER
+from app.api.deps import (
+    get_current_customer_from_cookie_or_header,  # HTML pages
+    get_current_customer_api,                     # API endpoints
+    get_current_customer_optional,                # Login pages
+)
+
+# GENERIC (any authenticated user)
+from app.api.deps import get_current_user  # Header-only, any role
+```
+
+## See Also
+
+- [Authentication Documentation](../api/authentication.md) - Complete auth system docs
+- [Authentication Flow Diagrams](../api/authentication-flow-diagrams.md) - Visual flows
+- [API Dependencies](../app/api/deps.py) - Source code
diff --git a/mkdocs.yml b/mkdocs.yml
index a7c7e5ab..a090636e 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -95,6 +95,7 @@ nav:
   - Development:
     - Icons Guide: development/icons_guide.md
     - Naming Conventions: development/naming-conventions.md
+    - Auth Dependencies Guide: development/AUTH_DEPENDENCIES_GUIDE.md
     - Database Migrations: development/database-migrations.md
     - Database Seeder:
       - Documentation: development/database-seeder/DATABASE_SEEDER_DOCUMENTATION.md