Provisioning a server on behalf of a user on GCP/AWS/Azure and probably relinquish access
Rather than provisioning resources on-behalf of a user which would require them exposing their credentials to you in some way, I would implement this using the various marketplaces:


Azure: Virtual Machine Offer Publishing
AWS: How to List Your Product in AWS
GCP: Sell on GCP


This has a couple of advantages:


It's fully automated, you are never exposed to their subscriptions thus you don't need to prove that you no longer have access - you never had it in the first place.
Everything is created within the customer's Subscription (Azure), Account (AWS) or Project (GCP) thus they bear all of the costs, you then get money from the cloud provider based upon how you price yourself in the marketplace.
You can generally create more than just a VM, i.e. you could create a PaaS Database for persistence.