Grafana & OpenID authentication problems

At the moment I’ve set up Grafana and my Identity Provider which is Gluu (https://www.gluu.org/).
I am using generic_oauth grafana module. Users should authenticate with Gluu and afterwards be redirected to Grafana.
I’ve created OpenID client and configured it to reach Grafana. But when I click log in with Gluu on Grafana page I get prompted to sign in with my Identity Provider and connection gets closed, i.e. “ERR_EMPTY_RESPONSE” in browser.
URL looks like this:

http://grafana.website:3000/login/generic_oauth?code=8533980d-f44c-4d64-a424-fbb439d25264&scope=openid&state=AqSDQ52%2B4GKbotqWMqFcYxrygbHcNTF%2B6PrSA15p%2Bm0%3D&session_state=62f39b4d-2d1d-4526-9175-f29d970a63c4

Redirect URL specified in Gluu: http://grafana.website:3000/login/generic_oauth

My oauth Grafana configuration:

allow_sign_up	true
allowed_domains	
allowed_organizations	
api_url	    https://gluu.website/oxauth/seam/resource/restv1/oxauth/userinfo
auth_url	https://gluu.website/oxauth/seam/resource/restv1/oxauth/authorize
client_id	@!E233.C3FC.11F4.6350!0001!A40B.5BVA!0008!7E52.CEEA.108E.C0G4
client_secret	************
enabled	true
hosted_domain	
name	Gluu
scopes	openid
team_ids	
tls_client_ca	
tls_client_cert	/etc/grafana/gluu_site.pem
tls_client_key	/etc/grafana/gluu_site.key
token_url	https://gluu.website/oxauth/seam/resource/restv1/oxauth/token

Couldn’t find any errors in gluu as well as in Grafana logs.
Could you please point me in the right direction? What am I missing?
Thanks in advance!

What does the api url, userinfo endpoint return? Looks like. It returns an empty response

It doesn’t return anything, in URL response I get code but no token… I wonder if my redirect_uri is valid. In Gluu I’ve got “Redirect Login URIs” set to
http://grafana.website:3000/login/generic_oauth . Is that right?