If you use an API, but in a way the author suggests (conformed to the UI, rather than an abstraction), what's the simpler/better way to do auth than API tokens?

If you use an API, but in a way the author suggests (conformed to the UI, rather than an abstraction), what's the simpler/better way to do auth than API tokens? I have depth of experience in a niche industry and I'm working to build solutions for that industry, but I'm still early on the learning curve of being an effective full stack developer to make those solutions.