Third party Idenification App and customer registration

[Knofan]

Hey guys!

Im about to implement BankID, an way to idenitfy a user in nordic countries. This is not an app in the normal sense and it does not integrate with shopify like a normal third party app would. There is no "install button" so to speak. 

We use javascript to make calls to the serivce and when the user has identifed him self the service returns an answer on who this person is. Then i will either create a customer profile if it does not alreay exist or, log the user into an existing. 

My dilemma is where to put the code to this. I have looked around a little but have not found a great example. Any ideas or perhaps someone can point me in the right direction? 

Thanks !