nginx ingress controller routing doesn't work as expected - nginx

Question

I have a kubernetes cluster with an application (deployment + ClusterIp service), nginx ingress controller, cert manager and letsencrypt issuer.
Here the service
apiVersion: v1
kind: Service
metadata:
name: myapp-service
namespace: mynamespace
spec:
selector:
app: myapp
ports:
- protocol: TCP
port: 80
targetPort: 80
type: ClusterIP
This is the the ingress yaml:
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: myapp-ingress
namespace: mynamespace
annotations:
kubernetes.io/ingress.class: nginx
cert-manager.io/cluster-issuer: letsencrypt
spec:
tls:
- hosts:
- <myapp>.<myregion>.cloudapp.azure.com
secretName: tls-secret
rules:
- host: <myapp>.<myregion>.cloudapp.azure.com
http:
paths:
- path: /
pathType: Prefix
backend:
service:
name: myapp-service
port:
number: 80
It works correctly, responding to the url https://<myapp>.<myregion>.cloudapp.azure.com.
Now I need to change the path like in :
spec:
tls:
- hosts:
- <myapp>.<myregion>.cloudapp.azure.com
secretName: tls-secret
rules:
- host: <myapp>.<myregion>.cloudapp.azure.com
http:
paths:
- path: /sub
pathType: Prefix
backend:
service:
name: myapp-service
port:
number: 80
I would expect to browse my app at https://<myapp>.<myregion>.cloudapp.azure.com/sub.
Instead I get
This <myapp>.<myregion>.cloudapp.azure.com page can’t be found
What I am doing wrong?
I tried to find examples online, but couldn't find any that helped me understand what's wrong.
EDIT
What happens behind the scenes (dev tools) is:
The browser sends a request to /sub
The ingress routes to the correct service, rewriting the url to /
The application receives the request correctly
The application wants to redirect the browser to a login url (e.g. /login)
The browser receives a redirect (302) to /login and executes it
The ingress doesn't see the /sub in the redirect url, so it doesn't know what to do
I guess the redirect url should be /sub/login, not simply /login.
There should be an easy way to configure the ingress to fix this trivial issue. Can someone point me to the right direction?