I also have same issue in 3.1 with G Suite OAuth2.
Web server tried: Apache with default configuration and also reverse proxy apache > nginx. Both with same result.
I can see same “authenticity_token” parameter with equal value in POST form data and form input:
<input type="hidden" name="authenticity_token" value="OXYpqPiOn70bMX4uyfK0bmtD+8O7clTIgQbl2LgSHnVdtZxPgbqgECu28H3ICVJ5WfJRjwDxoUoqFUIQrN8kNQ==">
I, [2019-09-17T16:06:29.552884 #7891-47016919858460] INFO -- : Started GET "/api/v1/online_notifications/?full=true&_=1568650566955" for 2a02:27a1:0:1::1 at 2019-09-17 16:06:29 +0300
I, [2019-09-17T16:06:29.561505 #7891-47016919858460] INFO -- : Processing by OnlineNotificationsController#index as JSON
I, [2019-09-17T16:06:29.561574 #7891-47016919858460] INFO -- : Parameters: {"full"=>"true", "_"=>"1568650566955"}
I, [2019-09-17T16:06:29.587197 #7891-47016919858460] INFO -- : Completed 200 OK in 26ms (Views: 7.3ms | ActiveRecord: 1.8ms)
I, [2019-09-17T16:06:33.480085 #7891-47016919858140] INFO -- : Started POST "/auth/google_oauth2" for 2a02:27a1:0:1::1 at 2019-09-17 16:06:33 +0300
F, [2019-09-17T16:06:33.485745 #7891-47016919858140] FATAL -- :
F, [2019-09-17T16:06:33.485792 #7891-47016919858140] FATAL -- : ActionController::InvalidAuthenticityToken (ActionController::InvalidAuthenticityToken):
F, [2019-09-17T16:06:33.485832 #7891-47016919858140] FATAL -- :
F, [2019-09-17T16:06:33.539005 #7891-47016919858140] FATAL -- : vendor/bundle/ruby/2.5.0/gems/omniauth-rails_csrf_protection-0.1.2/lib/omniauth/rails_csrf_protection/token_verifier.rb:34:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:209:in `request_call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:188:in `call!'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:169:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:192:in `call!'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:169:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:192:in `call!'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:169:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:192:in `call!'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/strategy.rb:169:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/omniauth-1.9.0/lib/omniauth/builder.rb:64:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/tempfile_reaper.rb:15:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/etag.rb:25:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/conditional_get.rb:38:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/head.rb:12:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/http/content_security_policy.rb:18:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/session/abstract/id.rb:232:in `context'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/session/abstract/id.rb:226:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/cookies.rb:670:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:98:in `run_callbacks'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/callbacks.rb:26:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/rack/logger.rb:38:in `call_app'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/rack/logger.rb:26:in `block in call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/tagged_logging.rb:71:in `block in tagged'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/tagged_logging.rb:28:in `tagged'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/tagged_logging.rb:71:in `tagged'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/rack/logger.rb:26:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/request_id.rb:27:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/method_override.rb:22:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/runtime.rb:22:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/executor.rb:14:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/actionpack-5.2.3/lib/action_dispatch/middleware/static.rb:127:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/rack-2.0.7/lib/rack/sendfile.rb:111:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:524:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/puma-3.12.1/lib/puma/configuration.rb:227:in `call'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/puma-3.12.1/lib/puma/server.rb:660:in `handle_request'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/puma-3.12.1/lib/puma/server.rb:474:in `process_client'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/puma-3.12.1/lib/puma/server.rb:334:in `block in run'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/puma-3.12.1/lib/puma/thread_pool.rb:135:in `block in spawn_thread'
[45d44153-b5c9-479b-accb-f8db9674a5da] vendor/bundle/ruby/2.5.0/gems/logging-2.2.2/lib/logging/diagnostic_context.rb:474:in `block in create_with_logging_context'