# Croct uses localStorage by default, how do I share identity across subdomains?

Asked by bram_v on 2025-08-18. Tags: cookies, identity, privacy.

We run www.example.nl and shop.example.nl. Current behavior: a reader who
crosses from www to shop shows up as a second anonymous profile, so their
reading history does not follow them into the shop.

Desired behavior: one profile across both subdomains.

I understand the default storage is localStorage, which I actually like from a
privacy standpoint, but localStorage is scoped per origin so I assume that is
the cause here. What is the supported way to bridge subdomains, and what
exactly do I need to configure

## 1 answer

### Answer from Dana Whitfield (2025-08-19)

localStorage is origin-scoped, exactly as you suspected, so www and shop each
get their own client ID and Croct sees two anonymous profiles. The supported
bridge is to switch identity storage to first-party cookies with a shared
domain.

The plug call takes a `cookie` option where you configure this per cookie:

```js
croct.plug({
    appId: 'YOUR_APP_ID',
    cookie: {
        clientId: {
            name: 'croct.id',
            domain: 'example.nl',
            maxAge: 31536000,
            secure: true,
        },
        userToken: {
            name: 'croct.user_token',
            domain: 'example.nl',
            secure: true,
        },
    },
});
```

The two cookies that matter are `croct.id` (the client ID) and
`croct.user_token`; a one-year `maxAge` is the typical choice for the client
ID. Setting `domain` to the apex makes both subdomains read the same
cookies, so the visitor is one profile everywhere. Each cookie also accepts
`path` and `sameSite` if your setup needs them.

These are still first-party cookies on your own domain, so the privacy
posture you like about the default does not really change, you are just
widening the scope from one origin to your own site family.