I'm often frustrated by no clear OAuth-like system for non general auth. Ie you have a server and a clientside JS app. How do you secure it? Cookies are the obvious thing to reach for, but in general i was never clear on exactly what the options are. What are pros and cons of various types of implementations? What are the do's and don'ts? And even if i use something i often felt i was implementing all of it (due to obscure languages choices frequently), but the specifics of the impl were often difficult to find.

It's embarrassing to say but auth has always confused me. And of course managers always instantly say "Just use OAuth" -_-