How to observe progress during a file upload may not be immediately obvious, when using Retrofit and OkHttp. We will build an implementation that uses a callback and then how to wrap it into a reactive stream.

Managing secret values in a way that doesn't make them easy to extract can be difficult. We will explore techniques we can apply to keep them out of source control and how to secure access to them.

Entities in our codebases will commonly need identifiers or IDs to refer to them with. We will have a look at the different options for them and how to make them type-safe, allowing our code to be safer and less error-prone.