Not a major issue but I was hoping the user password was stored in the OS Keyring if that is available (an option for that I suppose). But it does not seem to be the case.
First, your Zotero password isn't stored at all — it's converted to an API key, which can be used to access data but not to log in to the website.
The API key is stored in Zotero's equivalent of the Firefox login manager (Zotero is based on Firefox), which is to say, not plain-text, but ultimately readable if someone has access to your local files (though in that case you likely have other problems). You can view/remove access for a given API key from your settings.
Using an OS keyring isn't technically possible at the current time.
Upgrade Storage
The API key is stored in Zotero's equivalent of the Firefox login manager (Zotero is based on Firefox), which is to say, not plain-text, but ultimately readable if someone has access to your local files (though in that case you likely have other problems). You can view/remove access for a given API key from your settings.
Using an OS keyring isn't technically possible at the current time.