Code for blog post https://www.gabrielgamil.com/posts/firebase-custom-auth-sys-django/

app.js

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    console.log("User authenticated");
  } else {
    console.log("User lost");
  }
});

auth_views.py

class AuthenticateView(APIView):
  def post(self, request, format=None):
    serializer = AuthenticationSerializer(data=request.data)
    if serializer.is_valid():
      username = serializer.validated_data['username']
      password = serializer.validated_data['password']

      user = authenticate(request, username=username, password=password)
      if user is not None:

        additional_claims = {
            'tenant': str(user.userprofile.tenant.id)
        }
        custom_token = auth.create_custom_token(
            str(user.id), additional_claims)

        ts = TokenSerializer({'token': custom_token.decode('UTF-8')})
        return Response(ts.data, status=status.HTTP_200_OK)

    return Response(status=status.HTTP_406_NOT_ACCEPTABLE)

hooks1.js

const useFetchJWTFromDjangoApp = credentials => {
  const [authResponseData, setAuthResponseData] = useState({
    JWT: "",
    error: false
  });

  useEffect(() => {
    if (credentials) {
      fetch("/api/authenticate/", {
        method: "post",
        body: JSON.stringify(credentials),
        headers: {
          "Content-Type": "application/json"
        }
      })
        .then(response => {
          if (response.ok) {
            return response.json();
          }
          throw new Error("Network response bad.");
        })
        .then(data => {
          setAuthResponseData({ JWT: data.token, error: false });
        })
        .catch(error => {
          return setAuthResponseData({ JWT: "", error: true });
        });
    }
  }, [credentials]);
  return authResponseData;
};

hooks2.js

const useSignInWithCustomToken = (JWT, firebase) => {
  useEffect(() => {
    if (JWT && firebase) {
      firebase
        .signInWithToken(JWT)
        .then(() => {
          const base64Url = JWT.split(".")[1];
          const decodedValue = JSON.parse(atob(base64Url));
          localStorage.setItem("tenantId", decodedValue.claims.tenant);
        })
        .catch(function(error) {
          console.error("Error logging in: ", error);
        });
    }
  }, [JWT, firebase]);
};

models.py

class UserProfile(models.Model):
  user = models.OneToOneField(User, on_delete='CASCADE')
  tenant = models.ForeignKey(Tenant, on_delete='CASCADE')