Sequelize : How to map a custom attribute in a pivot table

I finally managed to achieve this by creating a model for the pivot table movie_person with the role attribute as a string.

var MoviePerson = sequelize.define("MoviePerson", {
    role: DataTypes.STRING
},
{
    tableName: 'movie_person',
    underscored: true
});

Then in my Movie model I added this

Movie.belongsToMany(models.Person, {
    through: models.MoviePerson,
    foreignKey: 'movie_id',
    as: 'persons'
});

I had to do something obviously similar to this in my Person model and that's it !