« AWS Cognito for SaaS businesses and IndieHackers

July 21, 2019


I recently launched a service to help SaaS businesses in Asia leverage SMS and WhatsApp to automate payment reminders and reduce customer churn. I use AWS Cognito for user registration and authentication.

AWS Cognito has 2 ways to manage users.

  • User Pool — Allows developers to add sign-up and sign-in functionality to web and mobile applications. It serves as your own identity provider and maintains a user directory in your own AWS account.
  • Identity Pool — Allows developers to use a third party identity service, such as facebook and google to add sign-up and sign-in functionality to web and mobile applications.

In this post, I’ll focus on user pools.

Why Cognito?

Cognito is a fully manages service and doesn’t require any hosting or maintenance. User pool was introduced in 2016 and the service and it’s API’s are mature at this point.

Here’s a list of features you get right out of the box with just a bit of configuration.

  • First 50,000 user signups are free and costs cents per user after that.
  • Option to use a hosted webpage for users to register and login. This allows you to add identity management to your website without having to design UI elements and flow for user Sign-up/Sign-In.
  • Support for using an email, phone number or a preferred specified username.
  • Automatically verify email addresses and phone numbers with a verification code.
  • Ability to add Authorization to API Gateway with a few lines of configuration.

Here’s a sample serverless framework file to help you get started: Github Gist

Custom Attributes

Cognito allows you to add up to 25 custom attributes to a user record. These don’t include the 17 standard attributes such as a username, email, timezone, address, etc.

This is useful for associating the user with special information such as an admin role, linking a child and parent account for single billing, a third party service id for federation, etc.

Note: Once added, a custom attribute cannot be changed or deleted.

Custom Authorizers

Custom authorizers are Lambda functions that are called before your main function to authenticate and/or authorize that the caller may proceed to your core function.

Cognito userpool already provides a default authorizer to confirm if he user is registered and if the username and password match whats on record, so why do we need a custom authorizer?

You would use this when you need to perform custom validations such as the following

  • Checking to make sure the users subscription is still active in a third party billing system.
  • Talking to a licensing server hosted on prem.
  • Any validation that goes beyond just checking to make sure the username and password are correct.

Cognito Triggers

Userpools triggers allow you to create custom workflows during user registration, authentication and token creation. There are currently 10 triggers. Some common use for triggers are:

  • Generate a custom message for users during email or phone number verification.
  • Migrate a user from one userpool to another.
  • Create custom authorizers.

Live Demo: https://aws-cognito-demo.netlify.app