Steps:

1. Create usergroup in foreman named "abc"
2. Configure keycloak with foreman as per instructions in https://www.theforeman.org/2018/06/using-saml-for-single-sign-on-to-foreman-through-keycloak.html and Create user in keycloak with same name "abc"
3. Try to login to foreman with user in keycloak

Results:

Oops, we're sorry but something went wrong Validation failed: A user group already exists with this name

and production.log showed

2019-03-12T06:04:08 [I|app|] Started GET "/users/extlogin" for IP at 2019-03-12 06:04:08 -0400
2019-03-12T06:04:08 [I|app|bd11a44a] Processing by UsersController#extlogin as HTML
2019-03-12T06:04:08 [W|app|bd11a44a] Action failed
ActiveRecord::RecordInvalid: Validation failed: A user group already exists with this name
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/validations.rb:80:in `raise_validation_error'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/validations.rb:52:in `save!'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/transactions.rb:315:in `block in save!'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/transactions.rb:387:in `block in with_transaction_returning_status'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:254:in `block in transaction'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/transaction.rb:239:in `block in within_new_transaction'
/opt/rh/rh-ruby25/root/usr/share/ruby/monitor.rb:226:in `mon_synchronize'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/transaction.rb:236:in `within_new_transaction'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/connection_adapters/abstract/database_statements.rb:254:in `transaction'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/transactions.rb:212:in `transaction'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/transactions.rb:385:in `with_transaction_returning_status'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/transactions.rb:315:in `save!'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/suppressor.rb:48:in `save!'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/persistence.rb:53:in `create!'
/usr/share/foreman/app/models/user.rb:304:in `block in find_or_create_external_user'
/usr/share/foreman/app/models/concerns/foreman/thread_session.rb:100:in `as'
/usr/share/foreman/app/models/concerns/foreman/thread_session.rb:106:in `as_anonymous_admin'
/usr/share/foreman/app/models/user.rb:302:in `find_or_create_external_user'
/usr/share/foreman/app/services/sso/apache.rb:38:in `authenticated?'
/usr/share/foreman/app/controllers/concerns/foreman/controller/authentication.rb:62:in `sso_authentication'
/usr/share/foreman/app/controllers/concerns/foreman/controller/authentication.rb:14:in `authenticate'
/usr/share/foreman/app/controllers/concerns/foreman/controller/authentication.rb:47:in `require_login'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:426:in `block in make_lambda'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:179:in `block (2 levels) in halting_and_conditional'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/abstract_controller/callbacks.rb:34:in `block (2 levels) in <module:Callbacks>'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:180:in `block in halting_and_conditional'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:513:in `block in invoke_before'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:513:in `each'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:513:in `invoke_before'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:107:in `block in run_callbacks'
/usr/share/foreman/app/models/concerns/foreman/thread_session.rb:32:in `clear_thread'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:118:in `block in run_callbacks'
/usr/share/foreman/app/controllers/concerns/foreman/controller/topbar_sweeper.rb:12:in `set_topbar_sweeper_controller'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:118:in `block in run_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/audited-4.7.1/lib/audited/sweeper.rb:14:in `around'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:118:in `block in run_callbacks'
/opt/theforeman/tfm/root/usr/share/gems/gems/audited-4.7.1/lib/audited/sweeper.rb:14:in `around'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:118:in `block in run_callbacks'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:136:in `run_callbacks'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/abstract_controller/callbacks.rb:41:in `process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal/rescue.rb:22:in `process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal/instrumentation.rb:34:in `block in process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/notifications.rb:168:in `block in instrument'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/notifications/instrumenter.rb:23:in `instrument'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/notifications.rb:168:in `instrument'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal/instrumentation.rb:32:in `process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal/params_wrapper.rb:256:in `process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activerecord-5.2.1/lib/active_record/railties/controller_runtime.rb:24:in `process_action'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/abstract_controller/base.rb:134:in `process'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionview-5.2.1/lib/action_view/rendering.rb:32:in `process'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal.rb:191:in `dispatch'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_controller/metal.rb:252:in `dispatch'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/routing/route_set.rb:52:in `dispatch'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/routing/route_set.rb:34:in `serve'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/journey/router.rb:52:in `block in serve'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/journey/router.rb:35:in `each'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/journey/router.rb:35:in `serve'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/routing/route_set.rb:840:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm/root/usr/share/gems/gems/apipie-rails-0.5.14/lib/apipie/static_dispatcher.rb:65:in `call'
/opt/theforeman/tfm/root/usr/share/gems/gems/apipie-rails-0.5.14/lib/apipie/extractor/recorder.rb:137:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/usr/share/foreman/lib/middleware/telemetry.rb:9:in `call'
/opt/theforeman/tfm/root/usr/share/gems/gems/apipie-rails-0.5.14/lib/apipie/middleware/checksum_in_headers.rb:27:in `call'
/usr/share/foreman/lib/middleware/catch_json_parse_errors.rb:8:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/tempfile_reaper.rb:15:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/etag.rb:25:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/conditional_get.rb:25:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/head.rb:12:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/http/content_security_policy.rb:18:in `call'
/usr/share/foreman/lib/middleware/logging_context.rb:23:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/session/abstract/id.rb:232:in `context'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/session/abstract/id.rb:226:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/cookies.rb:670:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/callbacks.rb:98:in `run_callbacks'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/callbacks.rb:26:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/railties-5.2.1/lib/rails/rack/logger.rb:38:in `call_app'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/railties-5.2.1/lib/rails/rack/logger.rb:28:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/sprockets-rails-3.2.1/lib/sprockets/rails/quiet_assets.rb:13:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/request_id.rb:27:in `call'
/opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.10.0.26/lib/katello/prevent_json_parsing.rb:12:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/method_override.rb:22:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/runtime.rb:22:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/activesupport-5.2.1/lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/executor.rb:14:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/actionpack-5.2.1/lib/action_dispatch/middleware/static.rb:127:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/sendfile.rb:111:in `call'
/opt/theforeman/tfm/root/usr/share/gems/gems/secure_headers-6.0.0/lib/secure_headers/middleware.rb:13:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/railties-5.2.1/lib/rails/engine.rb:524:in `call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/railties-5.2.1/lib/rails/railtie.rb:190:in `public_send'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/railties-5.2.1/lib/rails/railtie.rb:190:in `method_missing'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/urlmap.rb:68:in `block in call'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/urlmap.rb:53:in `each'
/opt/theforeman/tfm-ror52/root/usr/share/gems/gems/rack-2.0.5/lib/rack/urlmap.rb:53:in `call'
/usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/rack/thread_handler_extension.rb:77:in `process_request'
/usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:140:in `accept_and_process_next_request'
/usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler/thread_handler.rb:108:in `main_loop'
/usr/share/gems/gems/passenger-4.0.18/lib/phusion_passenger/request_handler.rb:441:in `block (3 levels) in start_threads'
/opt/theforeman/tfm/root/usr/share/gems/gems/logging-2.2.2/lib/logging/diagnostic_context.rb:474:in `block in create_with_logging_context'
2019-03-12T06:04:08 [I|app|bd11a44a] Deface: [WARNING] No :original defined for 'change 500 page content', you should change its definition to include:
:original => '35d2b4f7aac0c083740c6de6775473457e9ae9d8'
2019-03-12T06:04:08 [I|app|bd11a44a] Rendering common/500.html.erb within layouts/application
2019-03-12T06:04:08 [I|app|bd11a44a] Rendered common/500.html.erb within layouts/application (5.1ms)
2019-03-12T06:04:08 [I|app|bd11a44a] Rendered layouts/_application_content.html.erb (1.0ms)
2019-03-12T06:04:08 [I|app|bd11a44a] Deface: [WARNING] No :original defined for 'theme_resources', you should change its definition to include:
:original => '6c658d16f641b3b4c3e0a17b89fd7fec3a76b54a'
2019-03-12T06:04:08 [I|app|bd11a44a] Rendering layouts/base.html.erb
2019-03-12T06:04:08 [I|app|bd11a44a] Rendered layouts/base.html.erb (2.9ms)
2019-03-12T06:04:08 [I|app|bd11a44a] Completed 500 Internal Server Error in 45ms (Views: 27.5ms | ActiveRecord: 5.3ms)

Additional info: user wont be able to login again to foreman as it will always try to login with same user and displayed same error.