Can Trans Id be used as an untransmitted value to authenticate users?

[jagallout]

Hello!
I am developing the payment flow for a dedicated bitcoin retail store.
I want a way to allow users to anonymously purchase through the website, and as such need a substitute to a "username/password" login style workflow.

My thought was that I could use a combination of the following to allow the purchaser access to his goods:

Generate: Pay to address server side.
Generate: One time use passkey server side.

Once the payment has been verified, the user can use his server generated passkey AND the transaction ID to authenticate and display the purchased good.

As this is the first time I have tackled this problem I wanted to throw the idea by the community and see if I missed anything.

Thank you,
jagallout