Most remote APIs require some form of authorization in order to access them. We will explore using OkHttp Interceptors and Authorizers to authorize our web requests for use with OkHttp and Retrofit.

Kotlin makes creating properties that are initialized on first access very simple. We will go through different options for creating them and how they can be really useful in our Kotlin code.

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.