Exposed is an SQL library for Kotlin with DSL and DAO APIs for database interactions. While it comes with support for standard SQL data types, you can extend its functionality by creating custom column types.

Custom column types are useful when Exposed lacks support for specific database types (like PostgreSQL's enum, inet or ltree) or when you want to map columns to domain-specific types that better align with your business logic. By implementing custom columns, you gain control over data storage and retrieval while maintaining type safety.

In this article, we'll explore how to create custom column types in Exposed by creating a simple column type for PostgreSQL's enum.

Problem

Authorization is one of the first problems developers face upon starting a new project. And one of the most common types of authorization (from my experience) is the token-based authorization (usually using JWT).

From my perspective, this article looks like "what I wanted to read two weeks ago". My goal was to write minimalistic and reusable code with a clean and straightforward interface. I had the next requirements for my implementation of the auth management:

• Tokens should be stored in local storage
• Tokens should be restored on page reload
• Access token should be passed in the network requests
• After expiration access token should be updated by refresh token if the last one is presented
• React components should have access to the auth information to render appropriate UI
• The solution should be made with pure React (without Redux, thunk, etc..)