A cookie is a small piece of data sent from a website and stored by the web browser on the computer of a visitor, while browsing a website. The main purpose of a cookie is for websites to remember stateful information, or to record a visitor's browsing activity.
Cookies are usually small text files that are stored locally in the browser directory or program data subfolders. The website stores a corresponding file (with same ID tag).
## Cookies and Optimizely
Select the following sections to see how cookies are user in parts of the Optimizely platform.
[DXP cloud services](🔗)
[Optimizely Content Management System (CMS)](🔗)
[Optimizely Content Recommendations](🔗)
[Tracking, Profile Store (CDP), Visitor Intelligence]\(<https://docs.developers.optimizely.com/personalization/v1.3.0-tracking/docs/optimizely-tracking-cookies"Optimizely> Tracking Developer Guide")
[Marketing Automation connectors](🔗)
## SameSite cookies attributes
With version 80, Google Chrome implemented the changes the IETF has proposed for the SameSite cookie attribute. These are:
The default setting for cookies without a SameSite attribute changes from SameSite = None to SameSite = Lax.
When using SameSite = None, you must also specify **Secure**. Otherwise, the cookie is rejected. **Secure **requires communication over HTTPS.
To comply to these changes, Microsoft ASP.NET emits a SameSite cookie header when HttpCookie.SameSite value is **None**. As part of this change, **FormsAuth** and **SessionState** cookies are also issued with SameSite = Lax instead of the previous default value **None**.
See [Work with SameSite cookies in ASP.NET](🔗) for documentation on the changes in ASP.NET.
## Known issues - PDF preview for secured PDF
A bug in Chrome affects large PDFs with restricted access when SameSite = Lax for forms authentication. See the blog by Linus Ekström: [Issues with PDF preview for secured PDF:s in Google Chrome due to .NET security patch](🔗).
## Troubleshoot cookies
The new policy should work for most websites and cookies. Websites that cannot comply with the requirements of **Lax** have to change the default values. An example of a limitation with **Lax** is that you cannot iframe the site under another domain and still use cookie-based features such as authentication and session state.
Older browsers might not support SameSite or implement a different behavior on SameSite.
### Configure SameSite for anti-forgery
Configuring the built-in anti-forgery used in Optimizely user interface (requires **EPiServer.CMS.Core** 11.15):
### Configure SameSite for forms authentication
Configuring forms authentication to using **None** and HTTPS\:
### Configure SameSite for session state
Configuring session state to using **None**:
### Configure SameSite default values for cookies
Configuring the default for all cookies that do not explicitly use SameSite:
### Revert behavior of sending SameSite = None to browsers
Revert to the previous behavior of not sending SameSite = None to browsers:
[SameSite cookies explained](🔗)
[Azure App Service—SameSite cookie handling and .NET Framework 4.7.2 patch](🔗)
[Cumulative Update for .NET Framework](🔗)