$http_*

Description

In NGINX, the variable "$http_" is a dynamic prefix for accessing HTTP request headers sent by the client. The syntax for this variable is "$http_", where `` is converted to lowercase, and any dashes are replaced with underscores. For example, if the client sends a header `X-Forwarded-For`, you can access its value using `$http_x_forwarded_for`. This functionality enables NGINX to handle various headers conveniently, providing easy access to any HTTP header with a standard naming pattern. When a client makes a request to the server, all HTTP headers are available in the request context, and NGINX populates the `$http_` variables accordingly during the processing of the request. These variables can be utilized across various contexts in the configuration file, such as in `server`, `location`, and `if` blocks. Common headers accessed through this variable include authorization headers, custom application headers, and standard headers like `User-Agent` or `Accept-Encoding`, allowing for flexible request manipulation or conditional processing based on the presence or value of certain headers.

Config Example

server {
    listen 80;
    location /example {
        if ($http_user_agent ~* "Googlebot") {
            return 403;
        }
        add_header X-Your-Header "$http_x_your_header";
    }
}