Authenticating with client's login credentials

Hi Everyone I am hoping you can just point me in the right direction! My app has sub apps that will be on a client’s website by having them point a subdomain DNS to the sub app that i create for them. I have Bubble sub apps for each client. I would like users that are logged in via the clients authentication to be authenticated for my app (i.e. users should not need to login separately for my app).

Does anyone know the best/most common way to do this?