Laravel / Eloquent: How to create a primary key composed of two foreign keys?

I am creating a simple system for school management and I will have a table named 'student_class', where the primary key must be composed of the student id and class id, which are foreign keys of the 'student' and 'class' tables respectively . I created my migration as follows:

public function up()
{
    Schema::create('turma_alunos', function (Blueprint $table) {
        $table->integer('ID_TURMA_TUR')->unsigned();
        $table->foreign('ID_TURMA_TUR')->references('ID_TURMA_TUR')->on('turmas');
        $table->integer('ID_ALUNO_ALU')->unsigned();
        $table->foreign('ID_ALUNO_ALU')->references('ID_ALUNO_ALU')->on('alunos');
        $table->primary(['ID_TURMA_TUR', 'ID_ALUNO_ALU']);
        $table->timestamps();
    });
}

At the end, the table with the composite primary key was created, but only the student id was left as a foreign key:

Is it possible to do this the way I would like it? How to do this in Laravel?