concourse: Cannot login to Concourse Web using Firefox

Bug Report

When using Firefox, a login is not possible since the cookie cannot be set.

Steps to Reproduce

1. Deploy Concourse v4.2.3 (HTTPS enabled)
2. Use Firefox 65.0.2 to access the Concourse WEB UI
3. Login to concourse (tested with a local user and LDAP user)

(please include any pipelines/tasks using https://gist.github.com)

Expected Results

I expect to be successfully logged into concourse

Actual Results

After entering the username/password and submitting this page, a blank page is shown.

Additional Context

Logs in atc show that the login is successful. However, the error says that a cookie cannot be set.

/var/vcap/sys/log/atc/atc.stdout.log:

{"timestamp":"1551778162.090207577","source":"atc","message":"atc.dex.event","log_level":1,"data":{"fields":{},"message":"garbage collection run, delete auth requests=1, auth codes=0","session":"5"}}
{"timestamp":"1551781379.318979025","source":"atc","message":"atc.dex.event","log_level":1,"data":{"fields":{"connector":"LDAP"},"message":"performing ldap search DC=<....>","session":"5"}}
{"timestamp":"1551781379.320216894","source":"atc","message":"atc.dex.event","log_level":1,"data":{"fields":{"connector":"LDAP"},"message":"username \"<username>\" mapped to entry CN=<....>","session":"5"}}
{"timestamp":"1551781379.324945211","source":"atc","message":"atc.dex.event","log_level":1,"data":{"fields":{},"message":"login successful: connector \"ldap\", username=\"<username>\", email=\"<email>\", groups=[]","session":"5"}}
{"timestamp":"1551781379.332607746","source":"atc","message":"atc.sky.callback.failed-to-fetch-cookie-state","log_level":2,"data":{"error":"http: named cookie not present","session":"4.25"}}

This occurs only using firefox. It works well in chrome. I also checked if cookies are disabled in firefox but didn’t find anything. I explicitly allowed cookies for this domain and tried to turn off all security features that could be related to that.

Version Info

• Concourse version: 4.2.3
• Deployment type (BOSH/Docker/binary): BOSH
• Infrastructure/IaaS: vsphere
• Browser (if applicable): Firefox 65.0.2 It also works with latest Chrome version 72.0.3626.121
• Did this used to work? Yes