Cognito-mock NPM

Cognito Local

An offline emulator for Amazon Cognito.

The goal for this project is to be Good Enough for local development use, and that's it. Don't expect it to be perfect, because it won't be.

Features

At this point in time, assume any features listed below are partially implemented based on @jagregory's personal use-cases. If they don't work for you, please raise an issue.

Additional supported features:

JWKs verification
User Migration lambda trigger
Post Confirmation lambda trigger

Installation

yarn add --dev cognito-mock
# OR
npm install --dev cognito-mock

Usage

# if node_modules/.bin is in your $PATH
cognito-mock
# OR
yarn cognito-mock
# OR
npx cognito-mock

Cognito Local will now be listening on http://localhost:9229.

You can now update your AWS code to use the local address for Cognito's endpoint. For example, if you're using amazon-cognito-identity-js you can update your CognitoUserPool usage to override the endpoint:

new CognitoUserPool({
  /* ... normal options ... */
  endpoint: "http://localhost:9229/",
});

You likely only want to do this when you're running locally on your development machine.

Configuration

You do not need to supply a config unless you need to customise the behaviour of Congito Local. If you are using Lambda triggers, you will definitely need to override LambdaClient.endpoint at a minimum.

Before starting Cognito Local, create a config file:

mkdir .cognito && echo '{}' > .cognito/config.json

You can edit that .cognito/config.json and add any of the following settings:

Setting	Type	Default	Description
`LambdaClient`	`object`		Any setting you would pass to the AWS.Lambda Node.js client
`LambdaClient.credentials.accessKeyId`	`string`	`local`
`LambdaClient.credentials.secretAccessKey`	`string`	`local`
`LambdaClient.endpoint`	`string`	`local`
`LambdaClient.region`	`string`	`local`
`TriggerFunctions`	`object`	`{}`	Trigger name to Function name mapping
`TriggerFunctions.UserMigration`	`string`		User Migration lambda name
`UserPoolDefaults`	`object`		Default behaviour to use for the User Pool
`UserPoolDefaults.Id`	`string`	`local`	Default User Pool Id
`UserPoolDefaults.UsernameAttributes`	`string[]`	`["email"]`	Username alias attributes
`UserPoolDefaults.MfaConfiguration`	`string`		MFA type

The default config is:

{
  "LambdaClient": {
    "credentials": {
      "accessKeyId": "local",
      "secretAccessKey": "local"
    },
    "region": "local"
  },
  "TriggerFunctions": {},
  "UserPoolDefaults": {
    "Id": "local",
    "UsernameAttributes": ["email"]
  }
}

HTTPS endpoints with self-signed certificates

If you need your Lambda endpoint to be HTTPS with a self-signed certificate, you will need to disable certificate verification in Node for Cognito Local. The easiest way to do this is to run Cognito Local with the NODE_TLS_REJECT_UNAUTHORIZED environment variable.

NODE_TLS_REJECT_UNAUTHORIZED=0 cognito-mock

User Pools and Clients

User Pools are stored in .cognito/db/$userPoolId.json. As not all API features are supported yet, you'll likely find yourself needing to manually edit this file to update the User Pool config or users. If you do modify this file, you will need to restart Cognito Local.

User Pool Clients are stored in .cognito/db/clients.json. You can create new User Pool Clients using the CreateUserPoolClient API.

Known Limitations

Many. Cognito Local only works for my exact use-case.

Issues I know about:

Users can't be disabled
Only USER_PASSWORD_AUTH flow is supported
Not all Lambda triggers (yet, watch this space)

Multi-factor authentication

There is limited support for Multi-Factor Authentication in Cognito Local. Currently, if a User Pool is configured to have a MfaConfiguration of OPTIONAL or ON and a user has an MFAOption of SMS then Cognito Local will follow the MFA flows. If a user does not have a phone_number attribute or any other type of MFA is used, Cognito Local will fail.

Confirmation codes

When a user is prompted for a code of some kind (confirming their account, multi-factor auth), Cognito Local will write a message to the console with their confirmation code instead of emailing it to the user.

For example:

╭───────────────────────────────────────────────────────╮
│                                                       │
│   Confirmation Code Delivery                          │
│                                                       │
│   Username:    c63651ae-59c6-4ede-ae7d-a8400ff65e8d   │
│   Destination: example@example.com                    │
│   Code:        3520                                   │
│                                                       │
╰───────────────────────────────────────────────────────╯