Error 500 while trying to authenticate via Authentiq

GitLab CE Ominbus 10.8.0

I configured authentiq OmniAuth Provider as described here: [Gitlab Docs] Authentiq OmniAuth Provider.

When trying to sign in or linking an account with Authentiq I receive an Error 500 when Authentiq redirects me to:
https://MY_GITLAB_INSTANCE/users/auth/authentiq/callback

production.log:

Started GET "/users/auth/authentiq/callback?state=[FILTERED]&code=[FILTERED]&session_state=[FILTERED]" for ***.***.***.*** at 2018-05-22 18:46:48 +0200

NoMethodError (undefined method `decode' for OmniAuth::Strategies::JWT:Class):
  lib/gitlab/middleware/multipart.rb:95:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  lib/gitlab/middleware/go.rb:17:in `call'
  lib/gitlab/etag_caching/middleware.rb:11:in `call'
  lib/gitlab/middleware/read_only/controller.rb:28:in `call'
  lib/gitlab/middleware/read_only.rb:16:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
  lib/gitlab/middleware/release_env.rb:10:in `call'

Is this a bug (maybe related to GitLab CE Issue#45727: Omniauth JWT gem has incompatible JWT gem version) or did I miss something?