How do I set the OnConfiguring method in my DbContext without any hardcoded connection string?

I'm using multiple examples on how to set up my MySql service but in almost every one (including the Microsoft), they are using a hard coded connection string.

This is my startup:

    services.AddDbContext<DbContext>(options =>
    {
        options.UseMySql(configuration.GetConnectionString("DefaultConnection"),
        mysqlOptions =>
        {
            mysqlOptions.ServerVersion(new ServerVersion(new Version(8, 0, 18)));
        });
    });

And whenever I try to Update-Database I see an error telling me that there's no password setted

MySql.Data.MySqlClient.MySqlException (0x80004005): Access denied for user 'root'@'localhost' (using password: YES).

After looking around a bit I found an overrideable method called OnConfiguring, but I want to set the connection string in a dynamic way, cause If I change my environment, I want that string to change too.

This is where I found almost every example with hardcoded strings (ex. https://dev.mysql.com/doc/connector-net/en/connector-net-entityframework-core.html)