Prevent Facebook users who doesn't give consent for email with an Auth0 rule.

delete_facebook_users_without_email.js

function ( user, context, callback ) {
  
    // Only execute for Facebook Logins
    if ( context.connectionStrategy !== 'facebook' )
        return callback( null, user, context );
  
    // If User hasn't granted email permissions
    if ( typeof user.email === 'undefined' ) {

        // Load auth0 Management SDK
        const ManagementClient = require( 'auth0@2.13.0' ).ManagementClient;
        const management = new ManagementClient( {
            domain: auth0.domain,
            clientId: configuration.clientId,
            clientSecret: configuration.clientSecret,
            scope: 'delete:users'
        } );

        // Get Facebook Identity Details
        const facebookIdentity = _.find( user.identities, { connection: 'facebook' } );
        const fb_access_token = facebookIdentity.access_token;
        const fb_user_id = facebookIdentity.user_id;

        // throw error if no token has been found
        if ( typeof fb_access_token === 'undefined' )
            return callback( new UnauthorizedError( 'facebook_token_not_found' ) );

        // throw error if no facebook user id is given
        if ( typeof fb_user_id === 'undefined' )
            return callback( new UnauthorizedError( 'facebook_user_id_not_found' ) );

        // Make Delete App Request for the Facebook User so we can reauthorize it
        // @see https://developers.facebook.com/docs/graph-api/reference/user/permissions/#Deleting
        request.delete( `https://graph.facebook.com/v3.2/${ fb_user_id }/permissions`, {
            headers: {
                'Authorization': 'Bearer ' + fb_access_token
            }
        }, ( error, response, body ) => {

            if ( error || response.statusCode !== 200 )
                return callback( new UnauthorizedError( 'facebook_permission_error' ) );

            // Delete Auth0 user
            management.deleteUser( { id: user.user_id }, function( error ) {

                if ( error )
                    return callback( error );

                return callback( new UnauthorizedError( 'facebook_email_required' ) );           
            } );
        } );
    } else {
        // Proceed with login
        return callback( null, user, context );
    }
}