What query should be executed to confirm user registration?

Usually, this is a PUT or POST request to an address containing the confirmation token.

Example:

// On the client side
fetch('/api/auth/confirm-email', {
  method: 'PUT', // or POST
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({ token: 'received_token_from_link' })
})
.then(response => {
  if (!response.ok) {
    throw new Error('Confirmation error');
  }
  return response.json();
})
.then(data => {
  console.log('User confirmed:', data);
})
.catch(error => {
  console.error('Error:', error);
});

// On the server side (Node.js with Express)
app.put('/api/auth/confirm-email', async (req, res) => {
  const { token } = req.body;

  if (!token) {
    return res.status(400).json({ message: 'Token not provided' });
  }

  try {
    // Find user by token
    const user = await User.findOne({ confirmationToken: token });

    if (!user) {
      return res.status(404).json({ message: 'Invalid or expired token' });
    }

    // Set confirmation flag and clear token
    user.isConfirmed = true;
    user.confirmationToken = null; // Clear token after use
    user.confirmationTokenExpires = null; // Clear token expiry
    await user.save();

    res.status(200).json({ message: 'Email successfully confirmed' });

  } catch (error) {
    console.error('Email confirmation error:', error);
    res.status(500).json({ message: 'Server error during email confirmation' });
  }
});