I can make this map directive work:

map directive – allow origin

map $http_origin $allow_origin {
   ~^https?://localhost$      $http_origin;
   ~^https?://(www)?mysite.co.uk$ $http_origin;
   default "";
}

Equivalent if statement – allow origin:

if ($http_origin ~ '^https?://(localhost|mysite.co.uk)$') {
  $allow_origin=$http_origin;
}

Now I want to create another map directive based on the first one to determine if cred is true:

map directive – cred

map $http_origin $cred {
   '$allow_origin' true;
   default false;
}

Equivalent if statement – cred:

if ($http_origin ~ '^https?://(localhost|mysite.co.uk)$') {
  $cred=true;
}

But it always returns false
How can I fix this?
thanks