Feat: Add support for OAuth2 and OpenID Connect (OIDC) authentication (#7379)

### What problem does this PR solve?

Add support for OAuth2 and OpenID Connect (OIDC) authentication,
allowing OAuth/OIDC authentication using the specified routes:
- `/login/<channel>`: Initiates the OAuth flow for the specified channel
- `/oauth/callback/<channel>`: Handles the OAuth callback after
successful authentication

The callback URL should be configured in your OAuth provider as:
```
https://your-app.com/oauth/callback/<channel>
```

For detailed instructions on configuring **service_conf.yaml.template**,
see: `./api/apps/auth/README.md#usage`.

- Related issues
#3495  

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

api/apps/auth/README.md

@@ -0,0 +1,68 @@
+# Auth
+
+The Auth module provides implementations of OAuth2 and OpenID Connect (OIDC) authentication for integration with third-party identity providers. 
+
+**Features**
+
+- Supports both OAuth2 and OIDC authentication protocols
+- Automatic OIDC configuration discovery (via `/.well-known/openid-configuration`)
+- JWT token validation
+- Unified user information handling
+
+## Usage
+
+```python
+# OAuth2 configuration
+oauth_config = {
+    "type": "oauth2",
+    "client_id": "your_client_id",
+    "client_secret": "your_client_secret",
+    "authorization_url": "https://provider.com/oauth/authorize",
+    "token_url": "https://provider.com/oauth/token",
+    "userinfo_url": "https://provider.com/oauth/userinfo",
+    "redirect_uri": "https://your-app.com/oauth/callback/<channel>"
+}
+
+# OIDC configuration
+oidc_config = {
+    "type": "oidc",
+    "issuer": "https://provider.com/v1/oidc",
+    "client_id": "your_client_id",
+    "client_secret": "your_client_secret",
+    "redirect_uri": "https://your-app.com/oauth/callback/<channel>"
+}
+
+# Get client instance
+client = get_auth_client(oauth_config)  # or oidc_config
+```
+
+### Authentication Flow
+
+1. Get authorization URL:
+```python
+auth_url = client.get_authorization_url()
+```
+
+2. After user authorization, exchange authorization code for token:
+```python
+token_response = client.exchange_code_for_token(authorization_code)
+access_token = token_response["access_token"]
+```
+
+3. Fetch user information:
+```python
+user_info = client.fetch_user_info(access_token)
+```
+
+## User Information Structure
+
+All authentication methods return user information following this structure:
+
+```python
+{
+    "email": "user@example.com",
+    "username": "username",
+    "nickname": "User Name",
+    "avatar_url": "https://example.com/avatar.jpg"
+}
+```