How to send context to django models?

Question

Django

The form:

class CreatePostForm(ModelForm):
    class Meta:
        model = Post
        fields = ['title', 'text', 'spoiler']
        widgets = {
            'title': TextInput(attrs={
                'class': 'new-form-input',
                'placeholder': 'Header...'
            }),
            'text': Textarea(attrs={
                'class': 'comment-form',
                'placeholder': 'Text...'
            }
            ),
        }

Model:

class Post(models.Model):
    spoiler = models.ImageField(upload_to='user_images/')
    likes = models.IntegerField()
    title = models.CharField(max_length=200)
    text = models.TextField()
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    views = models.IntegerField()
    create_date = models.DateTimeField(auto_now_add=True)

    def get_absolute_url(self):
        return f'news/{self.id}'

    def __str__(self):
        return self.title

HTML form code:

<center>

    <div class="logo">
        <span class="re">Authorization</span> account<br>
    </div>
    {% if error %}
    <br>
    <div class="error">
        <span class="re" style="font-size: 20px;">Error</span><br><br>
        <span>{{ error }}</span>
    </div>
    {% endif %}
    <form method="post">
        {% csrf_token %}
        {{ form.username }}
        {{ form.password }}

        <p style="color: white;">You don't have account? - <a href="{% url 'registration' %}">registration</a></p>
        <button type="submit">Authorization </button>
        <br>
    </form>
</center>

Question:
I need to pass the error variable to the form, but how if only the form variable is passed in the class?