[MCP] Add auth status to MCP servers (#4918)

This adds a queryable auth status for MCP servers which is useful:
1. To determine whether a streamable HTTP server supports auth or not
based on whether or not it supports RFC 8414-3.2
2. Allow us to build a better user experience on top of MCP status

codex-rs/rmcp-client/src/oauth.rs

@@ -162,6 +162,14 @@ pub(crate) fn load_oauth_tokens(
     }
 }
 
+pub(crate) fn has_oauth_tokens(
+    server_name: &str,
+    url: &str,
+    store_mode: OAuthCredentialsStoreMode,
+) -> Result<bool> {
+    Ok(load_oauth_tokens(server_name, url, store_mode)?.is_some())
+}
+
 fn load_oauth_tokens_from_keyring_with_fallback_to_file<K: KeyringStore>(
     keyring_store: &K,
     server_name: &str,