code: def validate_token(self, token):
      '''retrieve a subject based on a token. Valid means we return a participant
         invalid means we return None
      '''
      from expfactory.database.models import Participant
      p = Participant.query.filter(Participant.token == token).first()
      if p is not None:
          if p.token.endswith(('finished','revoked')):
              p = None
          else:
              p = p.id
      return f validate_token(self, token):
      '''retrieve a subject based on a token. Valid means we return a participant
         invalid means we return None
      '''
      from expfactory.database.models import Participant
      p = Participant.query.filter(Participant.token == token).first()
      if p is not None:
          if p.token.endswith(('finished','revoked')):
              p = None
          else:
              p = p.id
      return p
docs: retrieve a subject based on a token. Valid means we return a participant
         invalid means we return None