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/create_client.html

@@ -0,0 +1,42 @@
+<style>
+  label, label > span { display: block; }
+  label { margin: 15px 0; }
+</style>
+
+<a href="/">Home</a>
+
+<form action="" method="post">
+  <label>
+    <span>Client Name</span>
+    <input type="text" name="client_name">
+  </label>
+  <label>
+    <span>Client URI</span>
+    <input type="url" name="client_uri">
+  </label>
+  <label>
+    <span>Allowed Scope</span>
+    <input type="text" name="scope">
+  </label>
+  <label>
+    <span>Redirect URIs</span>
+    <textarea name="redirect_uri" cols="30" rows="10"></textarea>
+  </label>
+  <label>
+    <span>Allowed Grant Types</span>
+    <textarea name="grant_type" cols="30" rows="10"></textarea>
+  </label>
+  <label>
+    <span>Allowed Response Types</span>
+    <textarea name="response_type" cols="30" rows="10"></textarea>
+  </label>
+  <label>
+    <span>Token Endpoint Auth Method</span>
+    <select name="token_endpoint_auth_method">
+      <option value="client_secret_basic">client_secret_basic</option>
+      <option value="client_secret_post">client_secret_post</option>
+      <option value="none">none</option>
+    </select>
+  </label>
+  <button>Submit</button>
+</form>