Fix IMDS token requests for managed identities (#6698)

This was broken by a035ee5f94, which
accidentally constructed the IMDS URL with a double slash at the start
of the path. This is not properly routed on the server side, leading to
a 404 error with some very misleading XML.

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

sdk/identity/azure-identity/CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Bugs Fixed
 
+- Fixed IMDS token requests for managed identities, which were broken by an invalid URL path in 1.12.0-beta.1.
+
 ### Other Changes
 
 ## 1.13.0 (2025-08-05)

sdk/identity/azure-identity/src/managed_identity_source.cpp

@@ -527,7 +527,7 @@ std::unique_ptr<ManagedIdentitySource> ImdsManagedIdentitySource::Create(
 
     imdsUrl = Core::Url{imdsEndpointEnvVarValue};
   }
-  imdsUrl.SetPath("/metadata/identity/oauth2/token");
+  imdsUrl.SetPath("metadata/identity/oauth2/token");
 
   return std::unique_ptr<ManagedIdentitySource>(
       new ImdsManagedIdentitySource(clientId, objectId, resourceId, imdsUrl, options));