title: Invalid signature in Django Rest Frameworl JWT
body: <p>I've created a custom login view to override obtain_jwt_token view as followed.</p>
  
  <pre><code>class LoginView(ObtainJSONWebToken):
      def post(self, request, *args, **kwargs):
          user = User.objects.using(self.request.session.get('shop')).get(mobile=str(request.data['mobile']))
          if not user.check_password(request.data['password']):
              return Response({'Error': "Invalid mobile or password"}, status="400")
          exp = datetime.datetime.now() + datetime.timedelta(seconds=settings.TOKEN_EXP_TIME)
          exp = int(datetime.datetime.timestamp(exp))
          orig_iat = int(datetime.datetime.timestamp(datetime.datetime.now()))
          if user:
              payload = {
                  'user_id': user.id,
                  "username": user.mobile,
                  "exp": exp,
                  "email": "",
                  'mobile': user.mobile,
                  "orig_iat": orig_iat
              }
             jwt_token = {'token': jwt.encode(payload, settings.SECRET_KEY)}
             return Response(jwt_token, status=status.HTTP_200_OK)
          else:
              return Response({'Error': "Invalid credentials"}, status=status.HTTP_400_BAD_REQUEST)
  
          response = super().post(request, *args, **kwargs)
          return response
  </code></pre>
  
  <p>after login token will created successfully but when I want to call an API (from postman) get <code>{"detail": "Invalid signature."}</code> error. </p>
  
  <p>I'm using my API using get method and I've added <code>JWT MY_TOKEN</code> in <code>Authorization</code> in header.
  Any idea?</p>