Pre sign-up Lambda trigger

Shortly before Amazon Cognito signs up a new user, it activates the pre sign-up AWS Lambda function. As part of the sign-up process, you can use this function to perform custom validation and, based on the results of your validation, accept or deny the registration request.

Pre sign-up Lambda flows

Client sign-up flow

Server sign-up flow

The request includes validation data from the client. This data comes from the ValidationData values passed to the user pool SignUp and AdminCreateUser API methods.

Pre sign-up Lambda trigger parameters

The request that Amazon Cognito passes to this Lambda function is a combination of the parameters below and the common parameters that Amazon Cognito adds to all requests.

JSON

{
    "request": {
        "userAttributes": {
            "string": "string",
            . . .
        },
        "validationData": {
            "string": "string",
            . . .
         },
        "clientMetadata": {
            "string": "string",
            . . .
         }
    },

    "response": {
        "autoConfirmUser": "boolean",
        "autoVerifyPhone": "boolean",
        "autoVerifyEmail": "boolean"
    }
}

Pre sign-up request parameters

userAttributes

One or more name-value pairs representing user attributes. The attribute names are the keys.

validationData

One or more key-value pairs with user attribute data that your app passed to Amazon Cognito in the request to create a new user. Send this information to your Lambda function in the ValidationData parameter of your AdminCreateUser or SignUp API request.

Amazon Cognito doesn't set your ValidationData data as attributes of the user that you create. ValidationData is temporary user information that you supply for the purposes of your pre sign-up Lambda trigger.

clientMetadata

One or more key-value pairs that you can provide as custom input to the Lambda function that you specify for the pre sign-up trigger. You can pass this data to your Lambda function by using the ClientMetadata parameter in the following API actions: AdminCreateUser, AdminRespondToAuthChallenge, ForgotPassword, and SignUp.

Pre sign-up response parameters

In the response, you can set autoConfirmUser to true if you want to auto-confirm the user. You can set autoVerifyEmail to true to auto-verify the user's email. You can set autoVerifyPhone to true to auto-verify the user's phone number.

Note

Response parameters autoVerifyPhone, autoVerifyEmail and autoConfirmUser are ignored by Amazon Cognito when the pre sign-up Lambda function is triggered by the AdminCreateUser API.

autoConfirmUser

Set to true to auto-confirm the user, or false otherwise.

autoVerifyEmail

Set to true to set as verified the email address of a user who is signing up, or false otherwise. If autoVerifyEmail is set to true, the email attribute must have a valid, non-null value. Otherwise an error will occur and the user will not be able to complete sign-up.

If the email attribute is selected as an alias, an alias will be created for the user's email address when autoVerifyEmail is set. If an alias with that email address already exists, the alias will be moved to the new user and the previous user's email address will be marked as unverified. For more information, see Customizing sign-in attributes.

autoVerifyPhone

Set to true to set as verified the phone number of a user who is signing up, or false otherwise. If autoVerifyPhone is set to true, the phone_number attribute must have a valid, non-null value. Otherwise an error will occur and the user will not be able to complete sign-up.

If the phone_number attribute is selected as an alias, an alias will be created for the user's phone number when autoVerifyPhone is set. If an alias with that phone number already exists, the alias will be moved to the new user and the previous user's phone number will be marked as unverified. For more information, see Customizing sign-in attributes.

Sign-up tutorials

The pre sign-up Lambda function is triggered before user sign-up. See these Amazon Cognito sign-up tutorials for JavaScript, Android, and iOS.

Platform	Tutorial
JavaScript Identity SDK	Sign up users with JavaScript
Android Identity SDK	Sign up users with Android
iOS Identity SDK	Sign up users with iOS

Pre sign-up example: Auto-confirm users from a registered domain

You can use the pre sign-up Lambda trigger to add custom logic that validates new users who sign up for your user pool. This is a sample JavaScript program that shows how to sign up a new user. It invokes a pre sign-up Lambda trigger as part of the authentication.

JavaScript

var attributeList = [];
var dataEmail = {
  Name: "email",
  Value: "...", // your email here
};
var dataPhoneNumber = {
  Name: "phone_number",
  Value: "...", // your phone number here with +country code and no delimiters in front
};

var dataEmailDomain = {
  Name: "custom:domain",
  Value: "example.com",
};
var attributeEmail = new AmazonCognitoIdentity.CognitoUserAttribute(dataEmail);
var attributePhoneNumber = new AmazonCognitoIdentity.CognitoUserAttribute(
  dataPhoneNumber
);
var attributeEmailDomain = new AmazonCognitoIdentity.CognitoUserAttribute(
  dataEmailDomain
);

attributeList.push(attributeEmail);
attributeList.push(attributePhoneNumber);
attributeList.push(attributeEmailDomain);

var cognitoUser;
userPool.signUp(
  "username",
  "password",
  attributeList,
  null,
  function (err, result) {
    if (err) {
      alert(err);
      return;
    }
    cognitoUser = result.user;
    console.log("user name is " + cognitoUser.getUsername());
  }
);

This is a sample Lambda trigger called just before sign-up with the user pool pre sign-up Lambda trigger. It uses a custom attribute custom:domain to automatically confirm new users from a particular email domain. Any new users not in the custom domain will be added to the user pool, but not automatically confirmed.

Node.js

exports.handler = (event, context, callback) => {
  // Set the user pool autoConfirmUser flag after validating the email domain
  event.response.autoConfirmUser = false;

  // Split the email address so we can compare domains
  var address = event.request.userAttributes.email.split("@");

  // This example uses a custom attribute "custom:domain"
  if (event.request.userAttributes.hasOwnProperty("custom:domain")) {
    if (event.request.userAttributes["custom:domain"] === address[1]) {
      event.response.autoConfirmUser = true;
    }
  }

  // Return to Amazon Cognito
  callback(null, event);
};

Python

def lambda_handler(event, context):
    # It sets the user pool autoConfirmUser flag after validating the email domain
    event['response']['autoConfirmUser'] = False

    # Split the email address so we can compare domains
    address = event['request']['userAttributes']['email'].split('@')

    # This example uses a custom attribute 'custom:domain'
    if 'custom:domain' in event['request']['userAttributes']:
        if event['request']['userAttributes']['custom:domain'] == address[1]:
            event['response']['autoConfirmUser'] = True

    # Return to Amazon Cognito
    return event

Amazon Cognito passes event information to your Lambda function. The function then returns the same event object to Amazon Cognito, with any changes in the response. In the Lambda console, you can set up a test event with data that is relevant to your Lambda trigger. The following is a test event for this code sample:

JSON

{
    "request": {
        "userAttributes": {
            "email": "[e-mail]",
            "custom:domain": "example.com"
        }
    },
    "response": {}
}

Pre sign-up example: Auto-confirm and auto-verify all users

This example confirms all users and sets the user's email and phone_number attributes to verified if the attribute is present. Also, if aliasing is enabled, aliases will be created for phone_number and email when auto-verify is set.

Note

If an alias with the same phone number already exists, the alias will be moved to the new user, and the previous user's phone_number will be marked as unverified. The same is true for email addresses. To prevent this from happening, you can use the user pools ListUsers API to see if there is an existing user who is already using the new user's phone number or email address as an alias.

Node.js

const handler = async (event) => {
  // Confirm the user
  event.response.autoConfirmUser = true;
  // Set the email as verified if it is in the request
  if (event.request.userAttributes.hasOwnProperty("email")) {
    event.response.autoVerifyEmail = true;
  }

  // Set the phone number as verified if it is in the request
  if (event.request.userAttributes.hasOwnProperty("phone_number")) {
    event.response.autoVerifyPhone = true;
  }

  return event;
};

export { handler };

Python

def lambda_handler(event, context):
    # Confirm the user
    event['response']['autoConfirmUser'] = True

    # Set the email as verified if it is in the request
    if 'email' in event['request']['userAttributes']:
        event['response']['autoVerifyEmail'] = True

    # Set the phone number as verified if it is in the request
    if 'phone_number' in event['request']['userAttributes']:
        event['response']['autoVerifyPhone'] = True

    # Return to Amazon Cognito
    return event

Amazon Cognito passes event information to your Lambda function. The function then returns the same event object to Amazon Cognito, with any changes in the response. In the Lambda console, you can set up a test event with data that is relevant to your Lambda trigger. The following is a test event for this code sample:

JSON

{
  "request": {
    "userAttributes": {
      "email": "[e-mail]",
      "phone_number": "[phone]"
    }
  },
  "response": {}
}

Pre sign-up example: Deny sign-up if user name has fewer than five characters

This example checks the length of the user name in a sign-up request. The example returns an error if the user has entered a name less than five characters long.

Node.js

exports.handler = (event, context, callback) => {
    // Impose a condition that the minimum length of the username is 5 is imposed on all user pools.
    if (event.userName.length < 5) {
        var error = new Error("Cannot register users with username less than the minimum length of 5");
        // Return error to Amazon Cognito
        callback(error, event);
    }
    // Return to Amazon Cognito
    callback(null, event);
};

Python

def lambda_handler(event, context):
    if len(event['userName']) < 5:
        raise Exception("Cannot register users with username less than the minimum length of 5")
    # Return to Amazon Cognito
    return event

Amazon Cognito passes event information to your Lambda function. The function then returns the same event object to Amazon Cognito, with any changes in the response. In the Lambda console, you can set up a test event with data that is relevant to your Lambda trigger. The following is a test event for this code sample:

JSON

{
  "userName": "rroe",
  "response": {}
}