docs: add next.js doc (#598)

docs/how-to-connect/nextjs.md

@@ -0,0 +1,142 @@
+---
+title: Next.js
+description: Using Casdoor in a Next.js project
+keywords: [nextjs]
+authors: [SamYSF]
+---
+
+[nextjs-auth](https://github.com/casdoor/nextjs-auth) is an example of how to integrate casdoor in a next-js project. We will guide you through the steps below.
+
+## Step 1: Deploy Casdoor
+
+Firstly, Casdoor should be deployed.
+
+You can refer to the Casdoor official documentation for the [Server Installation](/docs/basic/server-installation). Please deploy your Casdoor instance in **production mode**.
+
+After a successful deployment, make sure the following:
+
+- Open your favorite browser and visit **<http://localhost:8000>**. You will see the login page of Casdoor.
+- Test the login functionality by entering `admin` as the username and `123` as the password.
+
+After that, you can quickly implement a Casdoor-based login page in your own app using the following steps.
+
+## Step 2: Add Middleware
+
+Middleware allows you to run code before a request is completed. Then, based on the incoming request, you can modify the response by rewriting, redirecting, modifying the request or response headers, or responding directly.
+
+Use the file `middleware.ts` (or `.js`) in the root of your project to define Middleware. For example, at the same level as `pages` or `app`, or inside `src` if applicable.
+
+### Example
+
+```js
+//define which paths Middleware will run on
+const protectedRoutes = ["/profile"];
+
+export default function middleware(req) {
+  if (protectedRoutes.includes(req.nextUrl.pathname)) {
+    //redirect the incoming request to a different URL
+    return NextResponse.redirect(new URL("/login", req.url));
+  }
+}
+```
+
+See next.js official documentation [middleware](https://nextjs.org/docs/app/building-your-application/routing/middleware) for more details.
+
+## Step 3: Use Casdoor SDK
+
+### 1.Install the SDK
+
+First, install `casdoor-js-sdk` via NPM or Yarn:
+
+```shell
+npm install casdoor-js-sdk
+```
+
+Or:
+
+```shell
+yarn add casdoor-js-sdk
+```
+
+### 2.Initializing the SDK
+
+Then initialization 6 string-type parameters in the following order:
+
+| Name | Required | Description |
+|--------------------|----------|-----------------------------------------------------|
+| serverUrl | Yes | Casdoor Server URL, such as `http://localhost:8000` |
+| clientId | Yes | Application client ID |
+| clientSecret | Yes | Application client secret |
+| organizationName | Yes | Application organization |
+| appName | Yes | Application name |
+| redirectPath | Yes | redirected URL |
+
+### Example
+
+```js
+const sdkConfig = {
+  serverUrl: "https://door.casdoor.com",
+  clientId: "294b09fbc17f95daf2fe",
+  clientSecret: "dd8982f7046ccba1bbd7851d5c1ece4e52bf039d",
+  organizationName: "casbin",
+  appName: "app-vue-python-example",
+  redirectPath: "/callback",
+};
+```
+
+:::caution
+
+Replace the configuration values with your own Casdoor instance, especially the `clientId`, `clientSecret`, and `serverUrl`.
+
+:::
+
+### 3.Redirect to the Login Page
+
+When you need to authenticate users who access your app, you can send the target URL and redirect to the login page provided by Casdoor.
+
+Make sure you have added the callback URL (e.g. **<http://localhost:8080/callback>**) in the application configuration beforehand.
+
+```js
+const CasdoorSDK = new Sdk(sdkConfig);
+CasdoorSDK.signin_redirect();
+```
+
+### 4.Get Token and Storage
+
+After the Casdoor verification is passed, it will redirect back to your application with token.
+
+You can opt in to use cookie to storage the token.
+
+```js
+CasdoorSDK.exchangeForAccessToken()
+  .then((res) => {
+    if (res && res.access_token) {
+      //Get Token
+      return CasdoorSDK.getUserInfo(res.access_token);
+    }
+  })
+  .then((res) => {
+    // Storage Token
+    Cookies.set("casdoorUser", JSON.stringify(res));
+  });
+```
+
+You can refer to the Casdoor official documentation for the [How to use Casdoor SDK](https://casdoor.org/docs/how-to-connect/sdk/#how-to-use-casdoor-sdk).
+
+## Step 4: Add Middleware Authentication Function
+
+when users attempt to access a protected route, Middleware Authentication function verifies their identity. If the user is not authenticated, they are redirected to a login page or denied access.
+
+### Example
+
+```js
+//protected route
+const protectedRoutes = ["/profile"];
+const casdoorUserCookie = req.cookies.get("casdoorUser");
+const isAuthenticated = casdoorUserCookie ? true : false;
+
+//Authentication Function
+if (!isAuthenticated && protectedRoutes.includes(req.nextUrl.pathname)) {
+  return NextResponse.redirect(new URL("/login", req.url));
+}
+```

sidebars.js

@@ -73,6 +73,7 @@ module.exports = {
           ],
         },
         "how-to-connect/plugin",
+        "how-to-connect/nextjs",
         "how-to-connect/oauth",
         "how-to-connect/cas",
         {