How to Customize Emails in AWS Cognito

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import {Callback, Context} from 'aws-lambda';
import CustomMessage from './custom-message';

interface Event {
  triggerSource: string;
  request: {
    codeParameter: string;
    userAttributes: {
      'cognito:user_status': string;
      given_name: string;
      family_name: string;
      email: string;
    };
    usernameParameter: string;
  };
  response: {
    emailSubject: string;
    emailMessage: string;
  };
}

export function main(
  event: Event,
  _context: Context,
  callback: Callback,
): void {
  // 👇 in this case DOMAIN_NAME is provided via ENV var
  const {DOMAIN_NAME} = process.env;
  const {
    triggerSource,
    request: {codeParameter, userAttributes, usernameParameter},
  } = event;

  const customMessage = new CustomMessage({
    domainName: DOMAIN_NAME,
    userAttributes,
    codeParameter,
    usernameParameter,
  });

  /* eslint-disable no-param-reassign */
  if (
    triggerSource === 'CustomMessage_SignUp' &&
    userAttributes['cognito:user_status'] === 'UNCONFIRMED'
  ) {
    event.response = customMessage.sendCodePostSignUp();
  } else if (triggerSource === 'CustomMessage_ForgotPassword') {
    event.response = customMessage.sendCodeForgotPassword();
  } else if (triggerSource === 'CustomMessage_UpdateUserAttribute') {
    event.response = customMessage.sendCodeVerifyNewEmail();
  } else if (triggerSource === 'CustomMessage_AdminCreateUser') {
    event.response = customMessage.sendTemporaryPassword();
  } else if (triggerSource === 'CustomMessage_ResendCode') {
    event.response = customMessage.resendConfirmationCode();
  }

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

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interface CustomMessageProps {
  domainName: string;
  userAttributes: {
    given_name: string;
    family_name: string;
    email: string;
  };
  codeParameter: string;
  usernameParameter: string;
}

interface CustomMessage extends CustomMessageProps {}

interface CustomMessageMethod {
  emailSubject: string;
  emailMessage: string;
}

class CustomMessage {
  constructor(kwargs: CustomMessageProps) {
    Object.assign(this, kwargs);
  }

  sendCodePostSignUp(): CustomMessageMethod {
    return {
      emailSubject: `Validate your account for ${
        this.domainName
      } | ${new Date().toLocaleString()}`,
      emailMessage: `Hi <b>${this.userAttributes.given_name} ${this.userAttributes.family_name}</b>!
        <br>Thank you for signing up.
        <br />
       Please click on the link to activate your account:
        <a href="${this.domainName}/complete-registration?code=${this.codeParameter}&email=${this.userAttributes.email}">${this.domainName}</a>.
      `,
    };
  }

  sendCodeForgotPassword(): CustomMessageMethod {
    return {
      emailSubject: `Reset your password for ${
        this.domainName
      } | ${new Date().toLocaleString()}`,
      emailMessage: `Hi <b>${this.userAttributes.given_name} ${this.userAttributes.family_name}</b>!
      <br />
      Please click on the link to update your password:
        <a href="${this.domainName}/complete-password-reset?code=${this.codeParameter}&email=${this.userAttributes.email}">${this.domainName}</a>.
      `,
    };
  }

  sendCodeVerifyNewEmail(): CustomMessageMethod {
    return {
      emailSubject: `Validate your new email for ${
        this.domainName
      } | ${new Date().toLocaleString()}`,
      emailMessage: `Hi <b>${this.userAttributes.given_name} ${this.userAttributes.family_name}</b>!
      <br />
      Please click on the link to update your email address:
        <a href="${this.domainName}/complete-email-change?code=${this.codeParameter}">${this.domainName}</a>.
      `,
    };
  }

  sendTemporaryPassword(): CustomMessageMethod {
    return {
      emailSubject: `Your account for ${
        this.domainName
      } | ${new Date().toLocaleString()}`,
      emailMessage: `Hi User!<br>An administrator has created your credentials for ${this.domainName}.
      <br>Your username is <b>${this.usernameParameter}</b> and your temporary password is <b>${this.codeParameter}</b>
      <br>You can paste them in the form at <a href=${this.domainName}/login>${this.domainName}</a> in order to log in.`,
    };
  }

  resendConfirmationCode(): CustomMessageMethod {
    return {
      emailSubject: `Your sign-up confirmation link for ${
        this.domainName
      } | ${new Date().toLocaleString()}`,
      emailMessage: `Hi <b>${this.userAttributes.given_name} ${this.userAttributes.family_name}</b>!<br>Thank you for signing up.
      <br />
      Please click on the link to activate your account:
         <a href="${this.domainName}/complete-registration?code=${this.codeParameter}&email=${this.userAttributes.email}">${this.domainName}</a>.`,
    };
  }
}

export default CustomMessage;