How to hash a string in Nginx?

Currently in Nginx log_format we are logging entire request as aprt of $request. Sample Request :

test-registration.com/emp/reg?reqId=939393&usrName=Jimmy

Now our requirement is to extract the value of "reqId", hash that value and put the hashed value back to url So if the hashed reqID is ru64%$YYE&$&$ expected output should be :

test-registration.com/emp/reg?reqId=ru64%$YYE&$&$&usrName=Jimmy

I know we can extract the value of "reqId" by using map and regex which will be something like

 map $request $hashedReqId {
      "regular expression"  $requestId;
    }

But I am stuck in the next part.

My question is :

1) How to hash a string in Nginx ? Can we write Digest::SHA256.hexdigest str1 or somethig like this?

2) After hashing how to put it back to the url?

Please help me resolving this issue

Thanks