SMS message settings for Amazon Cognito user pools

Some Amazon Cognito events for your user pool might cause Amazon Cognito to send SMS text messages to your users. For example, if you configure your user pool to require phone verification, Amazon Cognito sends an SMS text message when a user signs up for a new account in your app or resets their password. Depending on the action that initiates the SMS text message, the message contains a verification code, a temporary password, or a welcome message.

Amazon Cognito uses Amazon Simple Notification Service (Amazon SNS) for delivery of SMS text messages. If you are sending a text message through Amazon Cognito or Amazon SNS for the first time, Amazon SNS places you in a sandbox environment. In the sandbox environment, you can test your applications for SMS text messages. In the sandbox, messages can be sent only to verified phone numbers.

Amazon SNS charges for SMS text messages. For more information, see Amazon SNS pricing.

Amazon Cognito sends SMS messages to your users with a code that they can enter. The following table shows the events that can generate an SMS message.

Message options

¹ For SMS messages.

Setting up SMS messaging for the first time in Amazon Cognito user pools

Amazon Cognito uses Amazon SNS to send SMS messages to your user pools. You can also use a Custom SMS sender Lambda trigger to use your own resources to send SMS messages. The first time that you set up Amazon SNS to send SMS text messages in a particular AWS Region, Amazon SNS places your AWS account in the SMS sandbox for that Region.Amazon SNS uses the sandbox to prevent fraud and abuse and to meet compliance requirements. When your AWS account is in the sandbox, Amazon SNS imposes some restrictions. For example, you can send text messages to a maximum of 10 phone numbers that you have verified with Amazon SNS. While your AWS account remains in the sandbox, do not use your Amazon SNS configuration for applications that are in production. When you're in the sandbox, Amazon Cognito can't send messages to your users' phone numbers.

Prepare an IAM role that Amazon Cognito can use to send SMS messages with Amazon SNS

When you send an SMS message from your user pool, Amazon Cognito assumes an IAM role in your account. Amazon Cognito uses the sns:Publish permission assigned to that role to send SMS messages to your users. In the Amazon Cognito console, you can set an IAM role selection from the Authentication methods menu of your user pool, under SMS or make this selection during the user pool creation wizard.

The following example IAM role trust policy grants Amazon Cognito user pools a limited ability to assume the role. Amazon Cognito can only assume the role when it meets the following conditions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Principal": {
                "Service": "cognito-idp.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringEquals": {
                    "sts:ExternalId": "a1b2c3d4-5678-90ab-cdef-EXAMPLE22222",
                    "aws:SourceAccount": "111122223333"
                },
                "ArnLike": {
                    "aws:SourceArn": "arn:aws:cognito-idp:us-west-2:111122223333:userpool/us-west-2_EXAMPLE"
                }
            }
        }
    ]
}

You can specify an exact user pool ARN or a wildcard ARN in the value of the aws:SourceArn condition. Look up the ARNs of your user pools in the AWS Management Console or with a DescribeUserPool API request.

To send SMS messages for multi-factor authentication, your IAM role trust policy must have an sts:ExternalId condition. The value of this condition must match the ExternalId property of the SmsConfiguration of your user pool. When you create an IAM role during the process of user pool creation in the Amazon Cognito console, Amazon Cognito configures the external ID for you in the role and in the user pool settings. This isn't true when you use an existing IAM role.

You must update the user pool ExternalId parameter in an UpdateUserPool API request and update the IAM role trust policy with an sts:externalId condition with the same value. To learn how to use the API to update a user pool in a way that preserves the original configuration, see Updating user pool and app client configuration.

For more information about IAM roles and trust policies, see Roles terms and concepts in the AWS Identity and Access Management User Guide.

Choose the AWS Region for Amazon SNS SMS messages

In some AWS Regions, you can choose the Region that contains the Amazon SNS resources that you want to use for Amazon Cognito SMS messages. In any AWS Region where Amazon Cognito is available, except for Asia Pacific (Seoul), you can use Amazon SNS resources in the AWS Region where you created your user pool. To make your SMS messaging faster and more reliable when you have a choice of Regions, use Amazon SNS resources in the same Region as your user pool.

Choose a Region for SMS resources in the Configure message delivery step of the new user pool wizard. You can also choose Edit under SMS in the Authentication methods menu of an existing user pool.

At launch, for some AWS Regions, Amazon Cognito sent SMS messages with Amazon SNS resources in an alternate Region. To set your preferred Region, use the SnsRegion parameter of the SmsConfigurationType object for your user pool. When you programmatically create an Amazon Cognito user pools resource in an Amazon Cognito Region from the following table and you do not provide an SnsRegion parameter, your user pool can send SMS messages with Amazon SNS resources in a legacy Amazon SNS Region.

Amazon Cognito user pools in the Asia Pacific (Seoul) AWS Region must use your Amazon SNS configuration in the Asia Pacific (Tokyo) Region.

Amazon SNS sets the spending quota for all new accounts at $1.00 (USD) per month. You might have increased your spend limit in an AWS Region that you use with Amazon Cognito. Before you change the AWS Region for Amazon SNS SMS messages, open a quota increase case in the AWS Support Center to increase your limit in the new Region. For more information, see Requesting increases to your monthly SMS spending quota for Amazon SNS in the Amazon Simple Notification Service Developer Guide.

You can send SMS messages for any Amazon Cognito Region in the following table with Amazon SNS resources in the corresponding Amazon SNS Region.

Obtain an origination identity to send SMS messages to US phone numbers

If you plan to send SMS text messages to US phone numbers, you must obtain an origination identity, regardless of whether you build an SMS sandbox testing environment, or a production environment.

Starting June 1, 2021, US carriers require an origination identity to send messages to US phone numbers. If you don't already have an origination identity, you must get one. To learn how to obtain an origination identity, see Requesting a number in the Amazon Pinpoint User Guide.

If you operate in the following AWS Regions, you must open an AWS Support ticket to obtain an origination identity. For instructions, see Requesting support for SMS messaging in the Amazon Simple Notification Service Developer Guide.

When you have more than one origination identity in the same AWS Region, Amazon SNS chooses an origination identity type in the following order of priority: short code, 10DLC, toll-free number. You can't change this priority. For more information, see Amazon SNS FAQs.

Confirm that you are in the SMS sandbox

Use the following procedure to confirm that you are in the SMS sandbox. Repeat for each AWS Region where you have production Amazon Cognito user pools.

Move your account out of Amazon SNS sandbox

If you are testing your app and you only need to send SMS messages to phone numbers that your administrators can verify, skip this step.

To use your app in production, move your account out of the SMS sandbox and into production. After you have configured an origination identity in the AWS Region that contains the Amazon SNS resources that you want Amazon Cognito to use, you can verify US phone numbers while your AWS account remains in the SMS sandbox. When your Amazon SNS environment is in production, you don't have to verify user phone numbers in Amazon SNS to send SMS messages to your users.

For detailed instructions, see Moving Out of the SMS Sandbox in the Amazon Simple Notification Service Developer Guide.

Verify phone numbers for Amazon Cognito in Amazon SNS

If you have moved your account out of the SMS sandbox, skip this step.

When you are in the SMS sandbox, you can send messages to any phone number that you have verified with Amazon SNS.

To verify a phone number, do the following:

For detailed instructions, see Adding and verifying phone numbers in the SMS sandbox in the Amazon Simple Notification Service Developer Guide.

Complete user pool setup in Amazon Cognito

Return to the browser tab where you were creating or editing your user pool. Complete the procedure. When you have successfully added SMS configuration to your user pool, Amazon Cognito sends a test message to an internal phone number to verify that your configuration works. Amazon SNS charges for each test SMS message.