doc: migrate more auth guide to v3

versioned_docs/version-3.x/recipe/auth-integration/better-auth.md

@@ -1,5 +1,6 @@
 ---
 sidebar_position: 1
+sidebar_label: Better-Auth
 ---
 
 import PackageInstall from '../../_components/PackageInstall';
@@ -25,7 +26,9 @@ Add the adapter to your better-auth configuration:
 
 ```ts
 import { zenstackAdapter } from '@zenstackhq/better-auth';
-import { db } from './db'; // your ZenStack ORM client
+
+// ZenStack ORM client
+import { db } from './db'; 
 
 const auth = new BetterAuth({
     database: zenstackAdapter(db, {
@@ -45,6 +48,8 @@ Then, run the "generate" command to generate the schema:
 
 <PackageExec command="@better-auth/cli generate" />
 
+You should see models like `User`, `Session`, and `Account` added to your `schema.zmodel` file if they don't already exist.
+
 Alternatively, you can refer to [better-auth schema documentation](https://www.better-auth.com/docs/concepts/database#core-schema) to manually add the necessary models.
 
 After the schema is configured, you can then use the regular ZenStack database schema migration workflow to push the schema to your database.
@@ -77,7 +82,10 @@ const userId = session.userId;
 Then you can pass it to `ZenStackClient`'s `$setAuth()` method to get a user-bound ORM client.
 
 ```tsx
-const userDb = db.$setAuth({ userId });
+// ZenStack ORM client with access policy plugin installed
+import { authDb } from './db'; 
+
+const userDb = authDb.$setAuth({ userId });
 ```
 
 ### Organization plugin support
@@ -109,7 +117,7 @@ After enabling the Organization plugin and running the CLI to generate the addit
 Then you can use the full `userContext` object to get a user-bound client.
 
 ```tsx
-const userDb = db.$setAuth(userContext);
+const userDb = authDb.$setAuth(userContext);
 ```
 
 The user context will be accessible in ZModel policy rules via the special `auth()` function. To get it to work, let's add a type in ZModel to define the shape of `auth()`:

versioned_docs/version-3.x/recipe/auth-integration/clerk.md

@@ -0,0 +1,68 @@
+---
+description: Integrating with Clerk.
+sidebar_position: 2
+sidebar_label: Clerk
+---
+
+# Clerk Integration
+
+[Clerk](https://clerk.com/) is a comprehensive authentication and user management platform, providing both APIs and pre-made UI components. This guide will show you how to integrate Clerk with ZenStack's [access control system](../../orm/access-control/).
+
+### Set up Clerk
+
+First, follow Clerk's [quick start guides](https://clerk.com/docs/quickstarts/overview) to set up your project if you haven't already.
+
+### Adjust your ZModel
+
+Since Clerk manages both user authentication and storage, you don't need to store users in your database anymore. However, you still need to provide a type that the `auth()` function can resolve to. Instead of using a regular model, we can declare a `type` instead:
+
+You can include any field you want in the `User` type, as long as you provide the same set of fields in the context object when calling `ZenStackClient`'s `$setAuth()` method.
+
+The following code shows an example blog post schema:
+
+```zmodel
+type User {
+  id String @id
+
+  @@auth
+}
+
+model Post {
+  id String @id @default(cuid())
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+  title String
+  published Boolean @default(false)
+  authorId String // stores Clerk's user ID
+
+  // author has full access
+  @@allow('all', auth() != null && auth().id == authorId)
+
+  // logged-in users can view published posts
+  @@allow('read', auth() != null && published)
+}
+```
+
+If you choose to [synchronize user data to your database](https://clerk.com/docs/users/sync-data-to-your-backend), you can define `User` as a regular `model` since it's then backed by a database table.
+
+### Create a user-bound ORM client
+
+When using ZenStack's built-in access control, you often use the `auth()` function in policy rules to reference the current user's identity. The evaluation of `auth()` at runtime requires you to call the `$setAuth()` method and pass in the validated user identity from Clerk. 
+
+Please refer to clerk's documentation on how to fetch the current user on the server side for your specific framework. The following code shows an example for Next.js (app router):
+
+```ts
+import { auth } from "@clerk/nextjs/server";
+
+// ZenStack ORM client with access policy plugin installed
+import { authDb } from './db'; 
+
+async function getUserDb() {
+  // get the validated user identity from Clerk
+  const authObject = await auth();
+
+  // create a user-bound ORM client
+  return authDb.$setAuth(
+    authObject.userId ? { id: authObject.userId } : undefined);
+}
+```

versioned_docs/version-3.x/recipe/auth-integration/custom.md

@@ -0,0 +1,59 @@
+---
+description: Integrating with a custom authentication system.
+sidebar_position: 100
+sidebar_label: Custom Authentication
+---
+
+# Custom Authentication Integration
+
+You may be using an authentication provider that's not mentioned in the guides. Or you may have a custom-implemented one. Integrating ZenStack with any authentication system is pretty straightforward. This guide will provide the general steps to follow.
+
+## Determine what's needed for access control
+
+The bridge that connects authentication and authorization is the `auth()` function that represents the authenticated current user. Based on your requirements, you should determine what fields are needed from it. The `auth()` object must at least contain an id field that uniquely identifies the current user. If you do RBAC, you'll very likely need an `auth().role` field available. Or even an `auth().permissions` field for fine-grained control.
+
+The `auth()` call needs to be resolved to a "model" or "type" in ZModel. If you store user data in your database, you may already have a "User" model that carries all the fields you need to access.
+
+```zmodel
+model User {
+  id          String @id
+  role        String
+  permissions String[]
+  ...
+}
+```
+
+ZenStack picks up the model named "User" automatically to resolve `auth()` unless another model or type is specifically appointed (by using the `@@auth` attribute). For example, if you're not storing user data locally, you can define a "type" to resolve `auth()`. This way, you can provide typing without being backed by a database table.
+
+```zmodel
+type Auth {
+  id          String @id
+  role        String
+  permissions String[]
+
+  @@auth
+}
+```
+
+Just remember that any thing that you access from `auth().` must be resolved.
+
+## Fetch the current user along with the additional information
+
+At runtime in your backend code, you need to provide a value for the `auth()` call to ZenStack, so it can use it to evaluate access policies. How this is done is solely dependent on your authentication mechanism. Here are some examples:
+
+1. If you use JWT tokens, you can issue tokens with user id and other fields embedded, then validate and extract them from the request.
+2. If you use a dedicated authentication service, you can call it to get the current user's information.
+
+You must ensure that whatever approach you use, the user information you get can be trusted and free of tampering.
+
+## Create a user-bound ORM client
+
+Finally, you can call the `$setAuth()` method on `ZenStackClient` to create an ORM instance that's bound to the current user. 
+
+```ts
+// ZenStack ORM client with access policy plugin installed
+import { authDb } from './db'; 
+
+const user = await getCurrentUser(); // your implementation
+const db = authDb.$setAuth(user);
+```