Fix authentication failures after going halfway through a sign-in attempt (#16607)

* Add tests

* Add security-related tests

My first (unpublished) attempt at fixing the issues introduced (extremely
hard-to-exploit) security vulnerabilities, addressing them in a test.

* Fix authentication failures after going halfway through a sign-in attempt

* Refactor `authenticate_with_sign_in_token` and `authenticate_with_two_factor` to make the two authentication steps more obvious

1 files changed, 12 insertions, 8 deletions

diff --git a/app/controllers/concerns/sign_in_token_authentication_concern.rb b/app/controllers/concerns/sign_in_token_authentication_concern.rb
index cbee84569..384c5c50c 100644
--- a/app/controllers/concerns/sign_in_token_authentication_concern.rb
+++ b/app/controllers/concerns/sign_in_token_authentication_concern.rb
@@ -16,14 +16,18 @@ module SignInTokenAuthenticationConcern
   end
 
   def authenticate_with_sign_in_token
-    user = self.resource = find_user
-
-    if user.present? && session[:attempt_user_id].present? && session[:attempt_user_updated_at] != user.updated_at.to_s
-      restart_session
-    elsif user_params.key?(:sign_in_token_attempt) && session[:attempt_user_id]
-      authenticate_with_sign_in_token_attempt(user)
-    elsif user.present? && user.external_or_valid_password?(user_params[:password])
-      prompt_for_sign_in_token(user)
+    if user_params[:email].present?
+      user = self.resource = find_user_from_params
+      prompt_for_sign_in_token(user) if user&.external_or_valid_password?(user_params[:password])
+    elsif session[:attempt_user_id]
+      user = self.resource = User.find_by(id: session[:attempt_user_id])
+      return if user.nil?
+
+      if session[:attempt_user_updated_at] != user.updated_at.to_s
+        restart_session
+      elsif user_params.key?(:sign_in_token_attempt)
+        authenticate_with_sign_in_token_attempt(user)
+      end
     end
   end