docs: def _get_token(self, oauth_request, token_type='access'):
          """Try to find the token for the provided request token key."""
          token_field = oauth_request.get_parameter('oauth_token')
          token = self.data_store.lookup_token(token_type, token_field)
          if not token:
              raise OAuthError('Invalid %s token: %s' % (token_type, token_field))
          return token