AWS Cognito username/email login is case-sensitive

Question

Setup

I am using AWS Cognito to manage the user registration and user access for my web application. Specifically I am using the Cognito hosted UI. This means that Cognito presents a UI for my users to register, I do not have access to modify the user sign-up or login pages for my application (other than the controls provided by Cognito). I am using email addresses as usernames, so new users are simply asked to provide an email address and password.

Problem

Cognito treats email addresses as case sensitive. If a user signs up with the email address [email protected], they cannot then sign in using [email protected].

I want user email addresses for sign-up and login to be case insensitive.

What I have tried

Usually this would be trivial to deal with by setting the email address to the lowercase in the client before sending it to the server. However I do not have access to the client UI as it is hosted by Cognito.

My plan therefore was to try using a Lambda function invoked by a Cognito pre-signup trigger to lowercase the email supplied by the user.

Pre sign-up

Amazon Cognito invokes this trigger when a user attempts to register (sign up), allowing you to perform custom validation to accept or deny the registration request.

Here is the lamdba function I wrote:

'use strict';

console.log('Loading function');

exports.handler = (event, context, callback) => {
    console.log('Received event:', JSON.stringify(event, null, 2));

    var triggerSource = event.triggerSource;
    console.log('Received triggerSource:', triggerSource);

    var email = event.request.userAttributes.email;
    console.log('Received email:', email);

    var modifiedEvent = event;

    if (email !== null) {
        var lowerEmail = email.toLowerCase();
        modifiedEvent.request.userAttributes.email = lowerEmail;
        console.log('Set email in request to', lowerEmail);
        console.log('Modified event:', JSON.stringify(modifiedEvent, null, 2));
    } else {
        console.log('Email evaluated as NULL, exiting with no action');
    }

    // Return result to Cognito
    callback(null, modifiedEvent);
};

This 'worked' in the sense that the email address in the event request was modified to be lowercase ([email protected]). However, it seems the account has already been created in the userpool by the time my Lambda function receives this event. Changing the email address in the request had no effect - the original email address ([email protected]) still appears in my user pool. I suspect the only fields in the event that have any effect are the response fields. Here is what my modified event looks like:

{
    "version": "1",
    "region": "us-east-1",
    "userPoolId": "us-east-1_xxxxxxx",
    "userName": "xxxxxx-xxxx-xxxx-xxxx-xxxxxxx",
    "callerContext": {
        "awsSdkVersion": "aws-sdk-java-console",
        "clientId": "xxxxxxxxxxxxxxxxxxxxxx"
    },
    "triggerSource": "PreSignUp_SignUp",
    "request": {
        "userAttributes": {
            "email": "[email protected]"
        },
        "validationData": null
    },
    "response": {
        "autoConfirmUser": false,
        "autoVerifyEmail": false,
        "autoVerifyPhone": false
    }
}

My question

I'm looking for ideas or examples to make my user registration and login case insensitive. This might include changes to my lambda trigger approach or something else entirely.

Please note I know I could implement my own UI, which I will only do as a last resort.

Answer 1

Fixed on new user pools. You can turn off case sensitivity now.

https://aws.amazon.com/about-aws/whats-new/2020/02/amazon-cognito-user-pools-service-now-supports-case-insensitivity-for-user-aliases/

Answer 2

You could trigger a Lambda function after sign-up to change the email to lowercase. Without actually testing it, you should be able to trigger a Lambda post confirmation. That Lambda could use AdminUpdateUserAttributes API, called from your SDK of choice, to change the email to lowercase.

Note that user names are also case sensitive.