During lazy migration, when import mode is active for a custom database, metadata passed in the "Login" and "Get User" actions intermittently fail to populate in the user profile. To resolve this issue, implement a post-login action that verifies the metadata is available and performs a one-time update if it is missing.

• Custom Database
• Lazy Migration
• Import Mode

To ensure metadata is always migrated from the custom database script, implement a post-login action that validates metadata availability and performs a one-time update if it is missing, using the provided sample code as a starting point.

const axios = require('axios');

exports.onExecutePostLogin = async (event, api) => {
  // 1. Check if the LEGACY_METADATA is already present
  // If it exists, exit early.
  if (event.user.app_metadata && event.user.app_metadata.LEGACY_METADATA) {
    return; 
  }

  // 2. If missing, fetch the data from the legacy system
  try {
    // NOTE: Replace this URL with the actual endpoint used to query your legacy database.
    // It's highly recommended to store API keys/tokens in Auth0 Action Secrets.
    const response = await axios.get('https://your-api.com/legacy-users', {
      params: { 
        email: event.user.email 
      },
      headers: {
        'Authorization': `Bearer ${event.secrets.LEGACY_API_SECRET}` 
      }
    });

    // Extract the information from your API's response payload
    const LEGACY_INFO = response.data.sub; // Adjust based on the actual API response

    // 3. Set the missing metadata on the Auth0 profile
    if (LEGACY_INFO) {
      api.user.setAppMetadata('LEGACY_METADATA', LEGACY_INFO);
    }

  } catch (error) {
    console.error('Failed to fetch LEGACY_INFO from legacy system:', error.message);
    
    // Optional: Deny the login if this metadata is strictly required for your apps to function
    // api.access.deny('Critical metadata missing. Please contact support.');
  }
};

After setting the metadata, the metadata becomes available in the event.user object during the next action. For the sample Action code provided, Auth0 stores the metadata at event.user.app_metadata.LEGACY_METADATA.