I need one account for each user due to each request is tied to that users not a global user for all users.
And I dont realy want to user “Service account”. Create a Service account for 1000s of custumers and keep there password sync to the Service account will be a problem.
For your mobile-app you will create a service account. For each user that want to login you will use the password grant OAuth2 flow to let the application directly passing the user credential and returning the token for the user.