docs: add Apple OAuth provider docs (#650)

Author: People257

docs/provider/oauth/apple.md

@@ -0,0 +1,57 @@
+---
+title: Apple
+description: Add the Apple Sign in OAuth provider to your application.
+keywords: [Apple, OAuth, Sign in with Apple]
+authors: [People257]
+---
+
+To set up the Apple Sign in provider, please go to the [Apple Developer](https://developer.apple.com/account) website. An active **Apple Developer Program membership** is required.
+
+### Step 1: Configure App ID
+
+Create a new App ID or configure an existing one, and ensure **Sign in with Apple** is enabled for it.
+
+![Enable Sign in with Apple for App ID](/img/providers/OAuth/appledashboard.png)
+
+### Step 2: Create a Services ID
+
+Next, create a new identifier, making sure to select the **Services IDs** type. (The `Identifier` you set here will be your **Client ID** in Casdoor).
+
+![Register Services ID](/img/providers/OAuth/appleregisterserviceid.png)
+
+Then, configure this Services ID. Enable **Sign in with Apple** and click **Configure**.
+
+![Edit Services ID Configuration](/img/providers/OAuth/appleeditserviceconfig.png)
+
+### Step 3: Configure Redirect URLs
+
+In the configuration screen, set up the **Return URLs** (callback URLs). You need to enter the **Redirect URL shown on the Casdoor provider page** here.
+
+![Configure Callback URLs](/img/providers/OAuth/applecallbackconfig.png)
+
+:::info Set Return URLs Correctly
+The `Return URLs` on Apple **must** exactly match the `Redirect URL` shown on your Casdoor Apple provider configuration page (e.g., `https://your-casdoor-domain.com/callback`).
+:::
+
+### Step 4: Create a Key
+
+After configuring the Services ID, create a **Key**.
+When creating the Key, enable **Sign in with Apple** and associate it with your App ID.
+
+![Configure Key Association](/img/providers/OAuth/applekeyconfig.png)
+
+After registering the Key, note down the **Key ID** and **download the `.p8` file immediately**. (This file can only be downloaded once, save it securely!)
+
+![Get Key ID and Download .p8 File](/img/providers/OAuth/applegetkeyid.png)
+
+**Important:** Find and note down your **Team ID** from the **Membership** page on the Apple Developer Portal.
+
+### Step 5: Configure Casdoor Provider
+
+1. **Client ID**: Enter the Apple **Services ID `Identifier`** you created earlier.
+2. **Team ID**: Enter your Apple **Team ID** (found on the Membership page).
+3. **Key ID**: Enter the Apple **Key ID** you noted down.
+4. **Key Text**: Open the downloaded `.p8` file with a text editor. Copy its **entire content** (including the `-----BEGIN...` and `-----END...` lines) and paste it here.
+5. **Check Redirect URL**: Verify that the `Redirect URL` shown here in Casdoor has been correctly added to the **Return URLs** in your Apple Services ID configuration.
+
+![Configure Casdoor Provider](/img/providers/OAuth/appleconfigcasdoor.png)

sidebars.js

@@ -169,6 +169,7 @@ module.exports = {
             "provider/oauth/github",
             "provider/oauth/linkedin",
             "provider/oauth/facebook",
+            "provider/oauth/apple",
             "provider/oauth/adfs",
             "provider/oauth/azureAD",
             "provider/oauth/azureADb2c",