Filter chain halted as :verify_authenticity_token rendered or redirected

[mferretti]

Hi,
I have been trying to understand the reason why I cannot use the plugin.
Here's the version information :

  Redmine version                4.0.5.stable.19090
  Ruby version                   2.5.1-p57 (2018-03-29) [x86_64-linux-gnu]
  Rails version                  5.2.3
  Environment                    production
  Database adapter               PostgreSQL
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
SCM:
  Subversion                     1.9.7
  Git                            2.17.1
  Filesystem                     
Redmine plugins:
  easy_gantt                     1.12
  redmine_checklists             3.1.14
  redmine_impersonate            1.0.0
  redmine_omniauth_saml          0.0.1
  redmine_zenedit                1.0.2

I have installed the plugin by clonng from GIT, then went into the plugin directory, ran bundle install and migrated the plugin as per instructions.

Looking at the production.log I see the SAML conversation starting and I see that WelcomeController is processing the SAML response but at the end it fails:

Processing by WelcomeController#index as HTML
  Parameters: {"SAMLResponse"=>"[hashed response]"}
Can't verify CSRF token authenticity.
  AnonymousUser Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."type" IN ('AnonymousUser') AND "users"."lastname" = $1 LIMIT $2  [["lastname", "Anonymous"], ["LIMIT", 1]]
  Rendering common/error.html.erb within layouts/base
  Rendered common/error.html.erb within layouts/base (0.8ms)
  Rendered plugins/redmine_zenedit/app/views/zenedit/_additional_assets.html.erb (0.0ms)
Filter chain halted as :verify_authenticity_token rendered or redirected
Completed 422 Unprocessable Entity in 14ms (Views: 10.7ms | ActiveRecord: 0.5ms)

Could you please point me as to what I am doing wrong ?

TIA