Plesk monitoring extension shows empty graphs: origin not allowed

Symptoms

• "No data" and "origin not allowed" messages are shown for graphs in Plesk > Monitoring:
  
  
• In an attempt to click the red triangle (as shown on the screenshot above) there is an error message:

  origin not allowed Objectstatus:403 statusText:"Forbidden" data:Objectmessage:"origin not allowed " error:"Forbidden" response:"origin not allowed " config:Objecturl:"api/datasources/proxy/2/query" data:Object method:"POST" withCredentials:false headers:Object retry:0 hideFromInspector:false message:"origin not allowed "

• The following messages can be found in /var/log/grafana/grafana.log:

  lvl=eror msg="Failed to look up user based on cookie" logger=context error="user token not found"
  lvl=eror msg="Request Completed" logger=context userId=0 orgId=0 uname= method=GET path=/login/generic_oauth status=500 remote_addr=127.0.0.1 time_ms=2 size=1383 referer="https://unikmedia.fr:8443/modules/grafana/service/d/monitoring__hdd/surveillance-disque?kiosk=tv&theme=light&orgId=1&refresh=2m"

• The Grafana extension was updated and now is 8.3.6:
  

  For CentOS/RHEL-based distributions

  # rpm -qa | grep grafana
  grafana-8.3.6-1.x86_64

  For Debian/Ubuntu-based distributions 
  

  # dpkg -l | grep grafana
  ii grafana 8.3.6 amd64 Grafana

  Cause

  This is a bug with ID #EXTPLESK-3382.
  Fixed in grafana-1.3.1-285.

  Resolution

  Update system packages via Tools & Settings > System Updates menu.

  Workaround

  1. Log into the server via SSH.
  2. Using the vi text editor open /etc/sw-cp-server/conf.d/grafana_plesk.inc file.
  3. Find change the line lines below from:
     

     location /modules/grafana/service/ {
         proxy_pass http://127.0.0.1:3030/;
         rewrite ^/modules/grafana/service/login$ /modules/grafana/service/login/generic_oauth redirect;
     }

     To

     location /modules/grafana/service/ {
         proxy_set_header Host $http_host;
         proxy_pass http://127.0.0.1:3030/;
         rewrite ^/modules/grafana/service/login$ /modules/grafana/service/login/generic_oauth redirect;
     }

  4. Save changes.
  5. Reload sw-cp-server to apply the changes:

     # systemctl reload sw-cp-server.service