title: Django form validation for a list of unknown strings
body: <p>I am working an API with Django REST framework. One of my API endpoints accepts the following post request:</p>
  
  <pre><code>{
      "tokens": ["biemnxci92j3kd", "xjcivjd23djcisd"],
      ...
  }
  </code></pre>
  
  <p>I want to use Django form to validate the parameters of this request. Here is my current form:</p>
  
  <pre><code>class TestForm(forms.Form):
      processors = forms.MultipleChoiceField()
      # other stuff
      ...
  </code></pre>
  
  <p>My problem is that the <code>MultipleChoiceField</code> requires me to provide a list of accepted choices, but the strings I accept have random values and I do not know their values beforehand. So validating this form always gives me an error. I thought of several possible solutions, but none of them seemed to work:</p>
  
  <ol>
  <li>Use another form field -- I cannot find another field that can be used to represent (and validate) a list of strings.</li>
  <li>Create my own custom validator -- This somehow still requires me to define the field as a multiple choice field beforehand, I'm not sure how to create my own custom string list field.</li>
  </ol>
  
  <p>Any suggestions?</p>