Hi @Kilian_Prevaes, welcome to the forum!
Your network firewall or proxy should allow access to the following domains:
*.asana.com*.sync.app.asana.com*.app.asana.com*.asanaops.net*.sentry.io(for error reporting)
I think that is all of them 
If you have an IT department, you may want someone from there to reach out to Support directly.