[dba-SQLServer] SQL calrification licensing

[J- P]

I have already put in a call to the  reseller (CDW) , but they seem pretty clueless , and they have told me we'll get back to you next week at some point "
 
 
Timeclock database  currently runs on backend sql server express, users access an IIS web server to login (badgeID and gpassword)
 
enter punch in punch out times. 
 
They want to go to full sql db-
 
What is the required /legal licensing for this?
 
Is it SQL per cpu  license and  an external connector license, or does does SQL require an external connector license?
 
if there are any vendors here,  they are open to discussion as CDW seemed pretty unclear