secure_link_md5

Defines an expression for which the MD5 hash value will be computed and compared with the value passed in a request.

The expression should contain the secured part of a link (resource) and a secret ingredient. If the link has a limited lifetime, the expression should also contain $secure_link_expires.

To prevent unauthorized access, the expression may contain some information about the client, such as its address and browser version.

Example:

location /s/ {
    secure_link $arg_md5,$arg_expires;
    secure_link_md5 "$secure_link_expires$uri$remote_addr secret";

    if ($secure_link = "") {
        return 403;
    }

    if ($secure_link = "0") {
        return 410;
    }

    ...
}

The “/s/link?md5=_e4Nc3iduzkWRm01TBBNYw&expires=2147483647” link restricts access to “/s/link” for the client with the IP address 127.0.0.1. The link also has the limited lifetime until January 19, 2038 (GMT).

On UNIX, the md5 request argument value can be obtained as:

echo -n '2147483647/s/link127.0.0.1 secret' | \
    openssl md5 -binary | openssl base64 | tr +/ -_ | tr -d =