Fetch metadata request header

A fetch metadata request header is an HTTP request header that provides additional information about the context from which the request originated. This allows the server to make decisions about whether a request should be allowed based on where the request came from and how the resource will be used.

With this information a server can implement a resource isolation policy, allowing external sites to request only those resources that are intended for sharing, and that are used appropriately. This approach can help mitigate common cross-site web vulnerabilities such as CSRF, Cross-site Script Inclusion (XSSI), timing attacks, and cross-origin information leaks.