Enable Chrome to share login credentials across affiliated sites

If you employ multiple domains that share the same account management backend, you can now also associate them with one another to enable users to save credentials once and have the Chrome password manager suggest them to any of the affiliated websites.

Milica Mihajlija

Chrome's password manager already autofills credentials for sites with saved credentials, as well as in the following two cases:

When two sites are in the same-site relationship, Chrome will show autofill credentials for the other site if there's at least one credential saved on one site. For example, because www.example.com and m.example.com are the same-site, Chrome can share saved credentials between the two sites and suggest the saved password to another.
When a developer associates an Android app with a site that uses the same credentials, Chrome can suggest Android credentials on that site. Apps are associated with sites using Digital Asset Links (DALs).

You can now also associate websites in a cross-site relationship to enable users to save their credentials once and have the password manager suggest them to any of the affiliated websites.

If you employ multiple domains that share the same account management backend (such as https://www.example.com and https://www.example.co.uk), starting in version 91, you can enable Chrome to suggest passwords saved to domains associated with Digital Asset Links.

To make a DAL association, developers need to put a JSON file that follows the DAL syntax at /.well-known/assetlinks.json on the respective domains.

Prerequisites

Use Chrome 91 or later.
Enable the flag at chrome://flags#filling-across-affiliated-websites.
Make sure "Offer to save passwords" is turned on in chrome://settings/passwords.
Make sure your website's sign-in domain is available through HTTPS.

Associate your two websites

To declare that the website, for example https://www.example.com,can share credentials with https://www.example.co.uk, create a file named assetlinks.json with the following content:
```
[{
  "relation": ["delegate_permission/common.get_login_creds"],
  "target": {
    "namespace": "web",
    "site": "https://www.example.com"
  }
 },
{
  "relation": ["delegate_permission/common.get_login_creds"],
  "target": {
    "namespace": "web",
    "site": "https://www.example.co.uk"
  }
}]
```
The relation field is an array of one or more strings that describe the relationship between the sites. For sites to share sign-in credentials, specify the string delegate_permission/common.get_login_creds. The target field is an object that specifies the asset the declaration applies to. The following fields identify a website:

namespace Must be web for websites.
site The website's URL, in the format https://domain[:optional_port]; for example, https://www.example.com.
See the Digital Asset Links reference for details.
Host the Digital Asset Links JSON file at the following location on the sign-in domain: https://domain[:optional_port]/.well-known/assetlinks.json.

In this example, the domain is www.example.com, so the JSON file should be hosted at https://www.example.com/.well-known/assetlinks.json.

The MIME type for the Digital Asset Links file needs to be JSON. Make sure the server sends a Content-Type: application/json header in the response.

Key point: The request for a DAL file must return an HTTP 200 OK status code, otherwise it will be treated as an error. This applies to redirects which return status codes in the 300-399 range.

To declare the association in both websites, host the assetlinks.jsonat https://www.example.co.uk/.well-known/assetlinks.json as well:

[{
  "relation": ["delegate_permission/common.get_login_creds"],
  "target": {
    "namespace": "web",
    "site": "https://www.example.com"
  }
 },
{
  "relation": ["delegate_permission/common.get_login_creds"],
  "target": {
    "namespace": "web",
    "site": "https://www.example.co.uk"
  }
}]

Ensure that your host permits Google to retrieve your Digital Asset Links file. If you have a robots.txt file, it must allow the Googlebot agent to retrieve /.well-known/assetlinks.json. Most sites can simply allow any automated agent to retrieve files in the /.well-known/ path so that other services can access the metadata in those files:
```
User-agent: *
Allow: /.well-known/
```

Associate multiple websites with one another

You can associate multiple websites with one another by specifying each one in the Digital Asset Links file. For example, to associate the example.com, example.co.uk,andexample.co.jp, specify all of those websites in the assetlinks.json JSON file and host it on each website at https://EXAMPLE_DOMAIN_NAME/.well-known/assetlinks.json.

[{
     "relation":[
        "delegate_permission/common.get_login_creds"
     ],
     "target":{
        "site":"https://www.example.com",
        "namespace":"web"
     }
  },
  {
     "relation":[
        "delegate_permission/common.get_login_creds"
     ],
     "target":{
        "site":"https://www.example.co.uk",
        "namespace":"web"
     }
  },
  {
     "relation":[
        "delegate_permission/common.get_login_creds"
     ],
     "target":{
        "site":"https://www.example.co.jp",
        "namespace":"web"
     }
  }]

`namespace`	Must be `web` for websites.
`site`	The website's URL, in the format `https://domain[:optional_port]`; for example, `https://www.example.com`.