Nginx: Reject request if header is not present or wrong

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You can use two IF statements either before or in the location block to inspect the headers and then return a 403 error code if it is present. Alternatively, you can use those IF statements to rewrite to a specific location block and deny all in that location:

if ($http_x_custom_header) {
    return 403;
}

Reference:
https://www.nginx.com/resources/wiki/start/topics/depth/ifisevil/
https://nginx.org/en/docs/http/ngx_http_access_module.html

Adding more detail per comment/request:

if ($http_x_custom_header) {
    return 405;
}

this looks to see if header exists

if you want to check to see if the correct values exist, then you first need to map the correct values to a variable. 

map $http_x_header $is_ok {
    default "0";
    Value1  "1";
    Value2  "1";
    Value3  "1";
}

if ($is_ok) {
    return 405; 
}

this first maps the header value to whether or not its ok, then checks to see if the variable is ok.

EDIT: Removed semicolon after map block since this causes an error.

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