Add H2H authentication service and new example flows

- Implement H2H authentication service for secure client authentication
- Add new examples for authorization code flow and H2H auth service
- Include example for generating client secret
- Update core connector and token request functionality
- Enhance README with new features

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

src/Requests/Auth/GetTokenRequest.php

@@ -42,6 +42,7 @@ class GetTokenRequest extends Request implements HasBody
         protected string $clientSecret,
         protected ?string $code = null,
         protected ?string $redirectUri = null,
+        protected ?string $refreshToken = null,
         protected string $grantType = 'authorization_code'
     ) {}
     // </SECTION>
@@ -64,11 +65,15 @@ class GetTokenRequest extends Request implements HasBody
             'client_secret' => $this->clientSecret,
         ];
         
-        if($this->grantType === 'authorization_code') {
+        if ($this->grantType === 'authorization_code') {
             $body['code'] = $this->code;
             $body['redirect_uri'] = $this->redirectUri;
         }
 
+        if ($this->grantType === 'refresh_token') {
+            $body['refresh_token'] = $this->refreshToken;
+        }
+
         return $body;
     }
     // </SECTION>