Amazon Cognito Construct Library

--- ![Stability: Experimental](https://img.shields.io/badge/stability-Experimental-important.svg?style=for-the-badge) > **This is a *developer preview* (public beta) module.** > > All classes with the `Cfn` prefix in this module ([CFN Resources](https://docs.aws.amazon.com/cdk/latest/guide/constructs.html#constructs_lib)) > are auto-generated from CloudFormation. They are stable and safe to use. > > However, all other classes, i.e., higher level constructs, are under active development and subject to non-backward > compatible changes or removal in any future version. These are not subject to the [Semantic Versioning](https://semver.org/) model. > This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package. ---

Amazon Cognito provides authentication, authorization, and user management for your web and mobile apps. Your users can sign in directly with a user name and password, or through a third party such as Facebook, Amazon, Google or Apple.

The two main components of Amazon Cognito are user pools and identity pools. User pools are user directories that provide sign-up and sign-in options for your app users. Identity pools enable you to grant your users access to other AWS services.

This module is part of the AWS Cloud Development Kit project.

User Pools

User pools allow creating and managing your own directory of users that can sign up and sign in. They enable easy integration with social identity providers such as Facebook, Google, Amazon, Microsoft Active Directory, etc. through SAML.

Using the CDK, a new user pool can be created as part of the stack using the construct’s constructor. You may specify the userPoolName to give your own identifier to the user pool. If not, CloudFormation will generate a name.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    user_pool_name="myawesomeapp-userpool"
)

Sign Up

Users can either be signed up by the app’s administrators or can sign themselves up. Once a user has signed up, their account needs to be confirmed. Cognito provides several ways to sign users up and confirm their accounts. Learn more about user sign up here.

When a user signs up, email and SMS messages are used to verify their account and contact methods. The following code snippet configures a user pool with properties relevant to these verification messages -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    self_sign_up_enabled=True,
    user_verification={
        "email_subject": "Verify your email for our awesome app!",
        "email_body": "Hello {username}, Thanks for signing up to our awesome app! Your verification code is {####}",
        "email_style": VerificationEmailStyle.CODE,
        "sms_message": "Hello {username}, Thanks for signing up to our awesome app! Your verification code is {####}"
    }
)

By default, self sign up is disabled. Learn more about email and SMS verification messages here.

Besides users signing themselves up, an administrator of any user pool can sign users up. The user then receives an invitation to join the user pool. The following code snippet configures a user pool with properties relevant to the invitation messages -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    user_invitation={
        "email_subject": "Invite to join our awesome app!",
        "email_body": "Hello {username}, you have been invited to join our awesome app! Your temporary password is {####}",
        "sms_message": "Your temporary password for our awesome app is {####}"
    }
)

All email subjects, bodies and SMS messages for both invitation and verification support Cognito’s message templating. Learn more about message templates here.

Sign In

Users registering or signing in into your application can do so with multiple identifiers. There are 4 options available:

  • username: Allow signing in using the one time immutable user name that the user chose at the time of sign up.

  • email: Allow signing in using the email address that is associated with the account.

  • phone: Allow signing in using the phone number that is associated with the account.

  • preferredUsername: Allow signing in with an alternate user name that the user can change at any time. However, this is not available if the username option is not chosen.

The following code sets up a user pool so that the user can sign in with either their username or their email address -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    # ...
    sign_in_aliases={
        "username": True,
        "email": True
    }
)

User pools can either be configured so that user name is primary sign in form, but also allows for the other three to be used additionally; or it can be configured so that email and/or phone numbers are the only ways a user can register and sign in. Read more about this here.

To match with ‘Option 1’ in the above link, with a verified email, signInAliases should be set to { username: true, email: true }. To match with ‘Option 2’ in the above link with both a verified email and phone number, this property should be set to { email: true, phone: true }.

Cognito recommends that email and phone number be automatically verified, if they are one of the sign in methods for the user pool. Read more about that here. The CDK does this by default, when email and/or phone number are specified as part of signInAliases. This can be overridden by specifying the autoVerify property.

The following code snippet sets up only email as a sign in alias, but both email and phone number to be auto-verified.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    # ...
    sign_in_aliases={"username": True, "email": True},
    auto_verify={"email": True, "phone": True}
)

Attributes

Attributes represent the various properties of each user that’s collected and stored in the user pool. Cognito provides a set of standard attributes that are available for all user pools. Users are allowed to select any of these standard attributes to be required. Users will not be able to sign up to the user pool without providing the required attributes. Besides these, additional attributes can be further defined, and are known as custom attributes.

Learn more on attributes in Cognito’s documentation.

The following code sample configures a user pool with two standard attributes (name and address) as required, and adds four optional attributes.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    required_attributes={
        "fullname": True,
        "address": True
    },
    custom_attributes={
        "myappid": StringAttribute(min_len=5, max_len=15),
        "callingcode": NumberAttribute(min=1, max=3),
        "is_employee": BooleanAttribute(),
        "joined_on": DateTimeAttribute()
    }
)

As shown in the code snippet, there are data types that are available for custom attributes. The ‘String’ and ‘Number’ data types allow for further constraints on their length and values, respectively.

Custom attributes cannot be marked as required.

Security

Cognito sends various messages to its users via SMS, for different actions, ranging from account verification to marketing. In order to send SMS messages, Cognito needs an IAM role that it can assume, with permissions that allow it to send SMS messages. By default, CDK will create this IAM role but can also be explicily specified to an existing IAM role using the smsRole property.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
from aws_cdk.aws_iam import Role

pool_sms_role = Role(self, "userpoolsmsrole")

UserPool(self, "myuserpool",
    # ...
    sms_role=pool_sms_role,
    sms_role_external_id="c87467be-4f34-11ea-b77f-2e728ce88125"
)

When the smsRole property is specified, the smsRoleExternalId may also be specified. The value of smsRoleExternalId will be used as the sts:ExternalId when the Cognito service assumes the role. In turn, the role’s assume role policy should be configured to accept this value as the ExternalId. Learn more about ExternalId here.

Multi-factor Authentication (MFA)

User pools can be configured to enable multi-factor authentication (MFA). It can either be turned off, set to optional or made required. Setting MFA to optional means that individual users can choose to enable it. Additionally, the MFA code can be sent either via SMS text message or via a time-based software token. See the documentation on MFA to learn more.

The following code snippet marks MFA for the user pool as required. This means that all users are required to configure an MFA token and use it for sign in. It also allows for the users to use both SMS based MFA, as well, time-based one time password (TOTP).

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    mfa=Mfa.REQUIRED,
    mfa_second_factor={
        "sms": True,
        "otp": True
    }
)

User pools can be configured with policies around a user’s password. This includes the password length and the character sets that they must contain.

Further to this, it can also be configured with the validity of the auto-generated temporary password. A temporary password is generated by the user pool either when an admin signs up a user or when a password reset is requested. The validity of this password dictates how long to give the user to use this password before expiring it.

The following code snippet configures these properties -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    password_policy={
        "min_length": 12,
        "require_lowercase": True,
        "require_uppercase": True,
        "require_digits": True,
        "require_symbols": True,
        "temp_password_validity": Duration.days(3)
    }
)

Note that, tempPasswordValidity can be specified only in whole days. Specifying fractional days would throw an error.

Emails

Cognito sends emails to users in the user pool, when particular actions take place, such as welcome emails, invitation emails, password resets, etc. The address from which these emails are sent can be configured on the user pool. Read more about email settings here.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
UserPool(self, "myuserpool",
    # ...
    email_transmission={
        "from": "noreply@myawesomeapp.com",
        "reply_to": "support@myawesomeapp.com"
    }
)

By default, user pools are configured to use Cognito’s built-in email capability, but it can also be configured to use Amazon SES, however, support for Amazon SES is not available in the CDK yet. If you would like this to be implemented, give this issue a +1. Until then, you can use the cfn layer to configure this.

Lambda Triggers

User pools can be configured such that AWS Lambda functions can be triggered when certain user operations or actions occur, such as, sign up, user confirmation, sign in, etc. They can also be used to add custom authentication challenges, user migrations and custom verification messages. Learn more about triggers at User Pool Workflows with Triggers.

Lambda triggers can either be specified as part of the UserPool initialization, or it can be added later, via methods on the construct, as so -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
auth_challenge_fn = lambda.Function(self, "authChallengeFn")

userpool = UserPool(self, "myuserpool",
    # ...
    triggers={
        "create_auth_challenge": auth_challenge_fn
    }
)

userpool.add_trigger(UserPoolOperation.USER_MIGRATION, lambda.Function(self, "userMigrationFn"))

The following table lists the set of triggers available, and their corresponding method to add it to the user pool. For more information on the function of these triggers and how to configure them, read User Pool Workflows with Triggers.

Importing User Pools

Any user pool that has been created outside of this stack, can be imported into the CDK app. Importing a user pool allows for it to be used in other parts of the CDK app that reference an IUserPool. However, imported user pools have limited configurability. As a rule of thumb, none of the properties that is are part of the ``AWS::Cognito::UserPool` <https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cognito-userpool.html>`_ CloudFormation resource can be configured.

User pools can be imported either using their id via the UserPool.fromUserPoolId(), or by using their ARN, via the UserPool.fromUserPoolArn() API.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
stack = Stack(app, "my-stack")

awesome_pool = UserPool.from_user_pool_id(stack, "awesome-user-pool", "us-east-1_oiuR12Abd")

other_awesome_pool = UserPool.from_user_pool_arn(stack, "other-awesome-user-pool", "arn:aws:cognito-idp:eu-west-1:123456789012:userpool/us-east-1_mtRyYQ14D")

App Clients

An app is an entity within a user pool that has permission to call unauthenticated APIs (APIs that do not have an authenticated user), such as APIs to register, sign in, and handle forgotten passwords. To call these APIs, you need an app client ID and an optional client secret. Read Configuring a User Pool App Client to learn more.

The following code creates an app client and retrieves the client id -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
pool = UserPool(self, "pool")
client = pool.add_client("customer-app-client")
client_id = client.user_pool_client_id

Existing app clients can be imported into the CDK app using the UserPoolClient.fromUserPoolClientId() API. For new and imported user pools, clients can also be created via the UserPoolClient constructor, as so -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
imported_pool = UserPool.from_user_pool_id(self, "imported-pool", "us-east-1_oiuR12Abd")
UserPoolClient(self, "customer-app-client",
    user_pool=imported_pool
)

Clients can be configured with authentication flows. Authentication flows allow users on a client to be authenticated with a user pool. Cognito user pools provide several several different types of authentication, such as, SRP (Secure Remote Password) authentication, username-and-password authentication, etc. Learn more about this at UserPool Authentication Flow.

The following code configures a client to use both SRP and username-and-password authentication -

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
pool = UserPool(self, "pool")
pool.add_client("app-client",
    auth_flows={
        "user_password": True,
        "user_srp": True
    }
)

Custom authentication protocols can be configured by setting the custom property under authFlow and defining lambda functions for the corresponding user pool triggers. Learn more at Custom Authentication Flow.

In addition to these authentication mechanisms, Cognito user pools also support using OAuth 2.0 framework for authenticating users. User pool clients can be configured with OAuth 2.0 authorization flows and scopes. Learn more about the OAuth 2.0 authorization framework and Cognito user pool’s implementation of OAuth2.0.

The following code configures an app client with the authorization code grant flow and registers the the app’s welcome page as a callback (or redirect) URL. It also configures the access token scope to ‘openid’. All of these concepts can be found in the OAuth 2.0 RFC.

# Example automatically generated without compilation. See https://github.com/aws/jsii/issues/826
pool = UserPool(self, "Pool")
pool.add_client("app-client",
    o_auth={
        "flows": {
            "authorization_code_grant": True
        },
        "scopes": [OAuthScope.OPENID],
        "callback_urls": ["https://my-app-domain.com/welcome"]
    }
)