Failed to authenticate usernamefrom trusted HTTP header via proxy

[gsmith]

@marif

but not able to authenticate users that were already created via old SSO plugin.

Yes this is true, for better clarity look here

EDIT:

@marif

is it something that this new SSO Model only works with Graylog Enterprise version?

Only the Trusted Header will work for Open source, but if you keep under 2Gb a day the Enterprise license is free.