Cookie Transmission Scenario Analysis

This document analyzes cookie transmission scenarios, organizing cookie transmission status according to various SameSite settings and domain attributes. This analysis is based on requests between https://api.hello.dev and https://hello.dev.

Prerequisites

All cookies have the following common options:

Secure=true: Cookies are only transmitted over HTTPS connections

Since browsers transmit all SameSite setting cookies only in requests between same sites (where origin and target share the same registered domain hello.dev), there is no blocking due to SameSite here. When a cookie's Domain attribute is specified, the cookie is transmitted to that domain and all its subdomains. In the tables below, ✅ indicates cookie transmission, and 🚫 indicates no transmission.

`https://api.hello.dev` → `https://api.hello.dev`

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	✅	✅	✅¹	✅¹
api.hello.dev	Lax	✅	✅	✅¹	✅¹
api.hello.dev	None	✅	✅	✅¹	✅¹
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

`https://api.hello.dev` → `https://*.hello.dev`

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	🚫	🚫	🚫	🚫
api.hello.dev	Lax	🚫	🚫	🚫	🚫
api.hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

`https://api.hello.dev` → `https://hello.dev`

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
api.hello.dev	Strict	🚫	🚫	🚫	🚫
api.hello.dev	Lax	🚫	🚫	🚫	🚫
api.hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

`https://hello.dev` → `https://api.hello.dev`

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
hello.dev	Strict	🚫	🚫	🚫	🚫
hello.dev	Lax	🚫	🚫	🚫	🚫
hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

`https://hello.dev` → `https://*.hello.dev`

Domain	SameSite	Form GET	Form POST	Fetch GET	Fetch POST
hello.dev	Strict	🚫	🚫	🚫	🚫
hello.dev	Lax	🚫	🚫	🚫	🚫
hello.dev	None	🚫	🚫	🚫	🚫
.hello.dev	Strict	✅	✅	✅¹	✅¹
.hello.dev	Lax	✅	✅	✅¹	✅¹
.hello.dev	None	✅	✅	✅¹	✅¹

Footnotes

¹ With credentials included (Fetch API requires credentials: include option)

Note: When a domain attribute is specified, cookies are transmitted to the specified domain and all its subdomains.

Cookie Transmission Scenario Analysis

Prerequisites

https://api.hello.dev → https://api.hello.dev

https://api.hello.dev → https://*.hello.dev

https://api.hello.dev → https://hello.dev

https://hello.dev → https://api.hello.dev