AWS Cognito with CloudFormation - InvalidParameterException on schema sttributes

Question

I'm trying to create a Cognito User Pool with CloudFormation but keep getting the following error upon creation:

Required custom attributes are not supported currently. (Service: AWSCognitoIdentityProviderService; Status Code: 400; Error Code: InvalidParameterException; Request ID: d21bec3f-adca-4c38-a91a-fa59f16a2cdc; Proxy: null)

The error message says I'm trying to create custom attributes but I'm just trying to specify behaviors for standard ones e.g. email, username, and preferred_username.

The AWS documentation is not helping much here. Any clue what's going on? See below my CF code:

  CognitoUserPool:
    Type: AWS::Cognito::UserPool
    Properties: 
      AccountRecoverySetting: # Defines which verified available method a user can use to recover their password when they call ForgotPassword
         RecoveryMechanisms:
          - Name: "verified_email"
            Priority: 1
      AdminCreateUserConfig: 
        AllowAdminCreateUserOnly: False
      Policies: 
        PasswordPolicy: 
          MinimumLength: 6
          RequireLowercase: False
          RequireNumbers: False
          RequireSymbols: False
          RequireUppercase: False
          TemporaryPasswordValidityDays: 7
      Schema: 
        - AttributeDataType: "String"
          Mutable: False
          Name: "email"
          Required: True
        - AttributeDataType: "String"
          Mutable: False
          Name: "username"
          Required: True
        - AttributeDataType: "String"
          Mutable: True
          Name: "preferred_username"
          Required: True
      UsernameAttributes: # This user pool property cannot be updated
        - "email"
      UserPoolName: !Sub "${ProjectName}-userPool-${BranchName}"

Thanks for your help, Joel

Answer 1

So... after reading everything more carefully, I realized username is kind of a strange attribute as it is not part of the list of standard attributes on the doc (here) but it is however always needed, as stated in the doc:

The username value is a separate attribute and not the same as the name attribute. A username is always required to register a user, and it cannot be changed after a user is created.

So I took out that attribute from the schema, thinking that anyway it would be there and that I could probably not change its properties. After that, it worked properly.