added client assertions sample link

Author: Erwinvandervalk

astro/src/content/docs/accesstokenmanagement/advanced/client-assertions.mdx

@@ -154,4 +154,6 @@ You need to explicitly set the `Audience` to the authorization server's issuer U
 
 Don't set the audience to the `TokenUrl`. Setting the `Audience` value to the token endpoint leaves 
 you vulnerable to these vulnerabilities: (CVE-2025-27370/CVE-2025-27371).
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+:::
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+For a complete working example, see the [WebClientAssertions sample](https://github.com/DuendeSoftware/foss/tree/main/access-token-management/samples/WebClientAssertions).