docs: update readme with openid certification badge

Author: steveiliop56

README.md

@@ -1,7 +1,7 @@
 <div align="center">
     <img alt="Tinyauth" title="Tinyauth" width="96" src="assets/logo-rounded.png">
     <h1>Tinyauth</h1>
-    <p>The tiniest authentication and authorization server you have ever seen.</p>
+    <p>The tiniest OpenID Certified™ authorization and authentication server you have ever seen.</p>
 </div>
 
 <div align="center">
@@ -28,6 +28,10 @@ Tinyauth is the simplest and tiniest authentication and authorization server you
 > [!NOTE]
 > This is the main development branch. For the latest stable release, see the [documentation](https://tinyauth.app) or the latest stable tag.
 
+As of 2026-06-25, Tinyauth v5.1.0 is OpenID Certified™ for Basic OP. You can find the certification details [here](https://openid.net/certification-old/certified-openid-providers-profiles/), test suite available [here](https://www.certification.openid.net/plan-detail.html?public=true&plan=H0qhpsOcQkxUE).
+
+<img alt="OpenID Certified" width="200" src="https://openid.net/wordpress-content/uploads/2016/05/oid-l-certification-mark-l-cmyk-150dpi-90mm.jpg" />
+
 ## Getting Started
 
 You can get started with Tinyauth by following the guide in the [documentation](https://tinyauth.app/docs/getting-started). There is also an available [docker-compose](./docker-compose.example.yml) file that has Traefik, Whoami and Tinyauth to demonstrate its capabilities (keep in mind that this file lives in the development branch so it may have updates that are not yet released).