Document HTTP_* parameter suppression in *_param directives - #309
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For fastcgi_param, uwsgi_param, and scgi_param, if the parameter name begins with HTTP_ and its value is set to an empty string, neither the parameter nor the corresponding client request header field is passed to the upstream server. This behaviour is a deliberate idiom for stripping a request header from what is forwarded to the backend, but had not been documented. Assisted-by: GitHub Copilot:claude-opus-4.7
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Adds a paragraph to the
fastcgi_param,uwsgi_param, andscgi_paramdirective documentation describing the empty-value HTTP_* suppression idiom.For all three modules, if a
*_paramdirective names a parameter beginning withHTTP_and gives it a literal empty string as its value, the parameter is not passed to the upstream server and the corresponding client request header field is also suppressed from auto-forwarding. This is a deliberate idiom (used e.g. to stripHTTP_AUTHORIZATIONbefore forwarding) but was not documented, leading to confusion — see nginx/nginx#484.Behaviour verified in
ngx_http_uwsgi_module.cL2192–2210,ngx_http_fastcgi_module.cL3478–3494, andngx_http_scgi_module.cL1869–1885.