Can't connect to heroku postgresql database from local node app with sequelize

OK, found the answer by browsing sequelize source code : https://github.com/sequelize/sequelize/blob/master/lib/dialects/postgres/connection-manager.js#L39

To activate SSL for PG connections you don't need native: true or ssl: true but dialectOptions.ssl: true so the following did finally work:

sequelize = new Sequelize(process.env.DATABASE_URL, {
    dialect: 'postgres',
    protocol: 'postgres',
    dialectOptions: {
        ssl: true
    }
});

You no longer need to parse the DATABASE_URL env variable, there is a Sequelize constructor which accepts the connection URL:

sequelize = new Sequelize(process.env.DATABASE_URL, {
    dialect: 'postgres',
    protocol: 'postgres',
    dialectOptions: {
        ssl: true
    }
});

One needs to add dialectOptions under ssl

 "development": {
    "username": process.env.DB_USERNAME,
    "password": process.env.DB_PASSWORD,
    "database": process.env.DB_NAME,
    "host": process.env.DB_HOST,
    "dialect": process.env.DB_DIALECT,
    "dialectOptions": {
        ssl: {
            require: true,
            rejectUnauthorized: false
        }
    }
},

Source is as per official sequelize github