best approach to LN payment verification?

I am trying to do payment verification in a web app. Assuming the web app user has received a lightning payment with a memo, is there a way for the web app to confirm payment/ look at that memo without an LN vendor's (alby) oauth2 ? I am a cheapskate and don't want that handshake traffic to go through the web server, but it looks like the way to get invoices is to do authentication with alby and get invoices.