feat: Add OAuth2 server and client implementation with PKCE support

- Implemented OAuth2 server with client registration, authorization, and token endpoints.
- Created HTML templates for client authorization, client creation, and client editing.
- Developed an OAuth2 client application using Hono.js and Bun, supporting authorization code grant flow.
- Integrated PKCE (Proof Key for Code Exchange) for enhanced security during authorization.
- Added session management using cookies for user authentication.
- Included detailed README documentation for setup and usage instructions.

example-oauth2-server/website/templates/home.html

@@ -0,0 +1,82 @@
+{% if user %}
+<style>
+pre{white-space:wrap}
+.client-container { 
+    border: 1px solid #ddd; 
+    padding: 15px; 
+    margin-bottom: 20px; 
+    border-radius: 5px; 
+    background-color: #f9f9f9; 
+}
+.client-actions { 
+    margin-top: 10px; 
+    padding-top: 10px; 
+    border-top: 1px solid #ccc; 
+}
+.client-actions a { 
+    margin-right: 10px; 
+    padding: 5px 10px; 
+    text-decoration: none; 
+    border-radius: 3px; 
+}
+.edit-btn { 
+    background-color: #007bff; 
+    color: white; 
+}
+.edit-btn:hover { 
+    background-color: #0056b3; 
+}
+.delete-btn { 
+    background-color: #dc3545; 
+    color: white; 
+}
+.delete-btn:hover { 
+    background-color: #c82333; 
+}
+.create-btn { 
+    background-color: #28a745; 
+    color: white; 
+    padding: 10px 20px; 
+    text-decoration: none; 
+    border-radius: 3px; 
+    display: inline-block; 
+    margin-top: 20px; 
+}
+.create-btn:hover { 
+    background-color: #218838; 
+}
+</style>
+<div>Logged in as <strong>{{user}}</strong> (<a href="{{ url_for('.logout') }}">Log Out</a>)</div>
+
+{% for client in clients %}
+<div class="client-container">
+<pre>
+<strong>Client Info</strong>
+  {%- for key in client.client_info %}
+  <strong>{{ key }}: </strong>{{ client.client_info[key] }}
+  {%- endfor %}
+<strong>Client Metadata</strong>
+  {%- for key in client.client_metadata %}
+  <strong>{{ key }}: </strong>{{ client.client_metadata[key] }}
+  {%- endfor %}
+</pre>
+    <div class="client-actions">
+        <a href="{{ url_for('.edit_client', client_id=client.id) }}" class="edit-btn">수정</a>
+        <form style="display: inline;" method="POST" 
+              action="{{ url_for('.delete_client', client_id=client.id) }}"
+              onsubmit="return confirm('정말로 이 클라이언트를 삭제하시겠습니까?')">
+            <button type="submit" class="delete-btn" 
+                    style="border: none; cursor: pointer; padding: 5px 10px; border-radius: 3px;">삭제</button>
+        </form>
+    </div>
+</div>
+{% endfor %}
+
+<a href="{{ url_for('.create_client') }}" class="create-btn">새 클라이언트 생성</a>
+
+{% else %}
+<form action="" method="post">
+  <input type="text" name="username" placeholder="username">
+  <button type="submit">Login / Signup</button>
+</form>
+{% endif %}