How can i add multiple callback url with oauth2

Hi, i am a php developer and i want your help, i want to do a dynamic callback urls with my connected app in salesforce. in WooCommerce Salesforce Integration plugin in api.php the callback url was http://www.crmperks.com/sf_auth/ i want to know how can that url manage different callback urls for multiple users who use different domains

because what i know is in salesforce connected app you have to specify an exact callback url with specific client url. what is the running code behind http://www.crmperks.com/sf_auth/ ? and how should i implement something like that for my plugin ?

Please Help and thank you !