how to remove quotation mark

[mangoo]

I've set a cookie with slash, so browser automatic add quotation marks to
the string.
So how to remove these quotation marks by following rule:
          set $path "";
          if ($http_cookie ~ "pp=([^;]+)(?:;|$)") {
             set  $path  $1;
          }
          sub_filter pp $path;

Firstly, set a cookie with value test/opt, and browser will set it to
"test/opt",
Then $http_cookie will get "test/opt". In fact, we don't need quotation
marks.

Definitely, these quotation marks should not be passed to $http_cookie.

How to avoid it?

Thanks in advance!

Regards
Mangoo