update-login-method.js

const loopback = require('loopback');

module.exports = function(app) {
  app.model(
    loopback.Model.extend(
      'LoginCredentials',
      {
        id: false,
        username: 'string',
        password: 'string'
      },
      { forceId: false, idInjection: false }
    )
  );

  updateLoginMethod(app);
};

function updateLoginMethod(app) {
  const login = app.models.User.sharedClass
    .methods()
    .find(item => item.name === 'login');
  Object.assign(login, {
    accepts: [
      {
        arg: 'credentials',
        type: 'LoginCredentials',
        required: true,
        http: { source: 'body' }
      }
    ],
    returns: [{ type: 'AccessToken', root: true }]
  });
  app.emit('modelRemoted');
}