You haven't said what you currently know, but here's some ideas: Security - even just understanding the various protocols and limitations of things like JWT wo

You haven't said what you currently know, but here's some ideas: Security - even just understanding the various protocols and limitations of things like JWT would be useful. Automated Testing - I'm a Test-Driven Development advocate, but I also know that's rarely easy to incorporate into existing codebases. However, the ability to write good, small, focused, developer tests is a very useful skill. And not just because of the tests, but often because it helps you implement functionality in smaller steps. HTTP API Design - Especially since it involves designing protocols without you realizing you're designing a protocol.