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 scripting ('XSSI') attacks, timing attacks, and cross-origin information leaks.
These headers are prefixed with Sec-, and hence have forbidden header names. As such, they cannot be modified from JavaScript.
