Working with APIs and writing web clients can be a tricky business. Different APIs have different types of authorization, authentication, and protocol. We'll explore the http.Client structure object, work with OAuth2 clients and long-term token storage, and finish off with GRPC and an additional REST interface.

By the end of this chapter, you should have an idea of how to interface with third-party or in-house APIs and have some patterns for common operations, such as async requests to APIs.

In this chapter, we will cover the following recipes:

• Initializing, storing, and passing http.Client structures
• Writing a client for a REST API
• Executing parallel and async client requests
• Making use of OAuth2 clients
• Implementing an OAuth2 token storage interface
• Wrapping a client in added functionality and function composition
• Understanding GRPC clients
• Using twitchtv/twirp for RPC