/usr/include/signon-extension/ is in signond-dev 8.58+16.04.20151106-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/signon-extension/SignOn/
/usr/include/signon-extension/SignOn/AbstractAccessControlManager
/usr/include/signon-extension/SignOn/AbstractCryptoManager
/usr/include/signon-extension/SignOn/AbstractKeyAuthorizer
/usr/include/signon-extension/SignOn/AbstractKeyManager
/usr/include/signon-extension/SignOn/AbstractSecretsStorage
/usr/include/signon-extension/SignOn/Debug
/usr/include/signon-extension/SignOn/ExtensionInterface
/usr/include/signon-extension/SignOn/KeyHandler
/usr/include/signon-extension/SignOn/abstract-access-control-manager.h
/usr/include/signon-extension/SignOn/abstract-crypto-manager.h
/usr/include/signon-extension/SignOn/abstract-key-authorizer.h
/usr/include/signon-extension/SignOn/abstract-key-manager.h
/usr/include/signon-extension/SignOn/abstract-secrets-storage.h
/usr/include/signon-extension/SignOn/debug.h
/usr/include/signon-extension/SignOn/export.h
/usr/include/signon-extension/SignOn/extension-interface.h
/usr/include/signon-extension/SignOn/key-handler.h