const authenticationData = {
  Username: user.email,
  Password: user.password,
};
const authenticationDetails = new AuthenticationDetails(authenticationData);
const userData = {
  Username: user.email,
  Pool: this.userPool
};
const cognitoUser = new CognitoUser(userData);
cognitoUser.authenticateUser(authenticationDetails, {
  onSuccess: function (session) {
    const tokens = {
      accessToken: session.getAccessToken().getJwtToken(),
      idToken: session.getIdToken().getJwtToken(),
      refreshToken: session.getRefreshToken().getToken()
    };
    cognitoUser['tokens'] = tokens; // Save tokens for later use
    resolve(cognitoUser); // Resolve user
  },
  onFailure: function (err) {
    return reject(err); // Reject out errors
  },
});