shared: add nm-secret-utils.h helper
We already had nm_free_secret() to clear the secret out of a NUL terminated string. That works well for secrets which are strings, it can be used with a cleanup attribute (nm_auto_free_secret) and as a cleanup function for a GBytes. However, it does not work for secrets which are binary. For those, we must also track the length of the allocated data and clear it. Add two new structs NMSecretPtr and NMSecretBuf to help with that.
Showing with 293 additions and 20 deletions