How to specify alphanumeric regex in kong

I want to expose one api which has some alpha numeric parameter in it.
API: http://web-url/lead/{tileid}
Here tileid is supposed to be alphanumeric character [A-Za-z0-9].

I tried with /lead/\w+ but here \w is more than just alpha-numeric.
I find [:alnum:] regex but don’t know how to specify that in kong. Its giving me invalid schema error.

Please help me here.