Update authorization.mdx

Author: localden

docs/specification/draft/basic/authorization.mdx

@@ -269,6 +269,8 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIs...
 
 MCP servers, acting in their role as an OAuth 2.1 resource server, **MUST** validate access tokens as described in
 [OAuth 2.1 Section 5.2](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1-12#section-5.2).
+MCP servers **MUST** validate that access tokens were issued specifically for them as the intended audience, 
+according to [RFC 8707 Section 2](https://www.rfc-editor.org/rfc/rfc8707.html#section-2).
 If validation fails, servers **MUST** respond according to
 [OAuth 2.1 Section 5.3](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1-12#section-5.3)
 error handling requirements. Invalid or expired tokens **MUST** receive a HTTP 401
@@ -359,9 +361,11 @@ MCP servers **MUST** validate access tokens before processing the request, ensur
 
 A MCP server **MUST** follow the guidelines in [OAuth 2.1 - Section 5.2](https://www.ietf.org/archive/id/draft-ietf-oauth-v2-1-12.html#section-5.2) to validate inbound tokens.
 
-MCP servers **MUST** only accept tokens specifically intended for themselves.
+MCP servers **MUST** only accept tokens specifically intended for themselves and **MUST** reject tokens that do not include them in the audience claim or otherwise verify that they are the intended recipient of the token. See [Security Best Practices](../security_best_practices) for details.
 
 If the MCP server makes requests to upstream APIs, it may act as an OAuth client to them. The access token used at the upstream API is a seperate token, issued by the upstream authorization server. The MCP server **MUST NOT** pass through the token it received from the MCP client.
 
-MCP clients **MUST** implement and use the `resource` parameter as defined in [RFC 8707 - Resource Indicators for OAuth 2.0](https://www.rfc-editor.org/rfc/rfc8707.html) to explicitly specify the target resource for which the token is being requested.
-This ensures that access tokens are bound to their intended resources and cannot be misused across different services.
+MCP clients **MUST** implement and use the `resource` parameter as defined in [RFC 8707 - Resource Indicators for OAuth 2.0](https://www.rfc-editor.org/rfc/rfc8707.html)
+to explicitly specify the target resource for which the token is being requested. This requirement aligns with the recommendation in 
+[RFC 9728 Section 7.4](https://datatracker.ietf.org/doc/html/rfc9728#section-7.4). This ensures that access tokens are bound to their intended resources and
+cannot be misused across different services.