fix: strip trailing slash from resource URL in get_resource_url()

Pydantic v2 AnyHttpUrl adds a trailing slash to bare-domain URLs when
str() is called, causing audience mismatch with Entra ID v2.0 which
registers the resource without a trailing slash.

Fixes #2578

Author: siddhirajk

src/mcp/client/auth/oauth2.py

@@ -151,7 +151,7 @@ def get_resource_url(self) -> str:
 
         # If PRM provides a resource that's a valid parent, use it
         if self.protected_resource_metadata and self.protected_resource_metadata.resource:
-            prm_resource = str(self.protected_resource_metadata.resource)
+            prm_resource = str(self.protected_resource_metadata.resource).rstrip("/")
             if check_resource_allowed(requested_resource=resource, configured_resource=prm_resource):
                 resource = prm_resource