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My first (unpublished) attempt at fixing the issues introduced (extremely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, 13 insertions, 9 deletions

diff --git a/app/controllers/concerns/two_factor_authentication_concern.rb b/app/controllers/concerns/two_factor_authentication_concern.rb
index 909ab7717..2583d324b 100644
--- a/app/controllers/concerns/two_factor_authentication_concern.rb
+++ b/app/controllers/concerns/two_factor_authentication_concern.rb
@@ -35,16 +35,20 @@ module TwoFactorAuthenticationConcern
   end
 
   def authenticate_with_two_factor
-    user = self.resource = find_user
+    if user_params[:email].present?
+      user = self.resource = find_user_from_params
+      prompt_for_two_factor(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 user.present? && session[:attempt_user_id].present? && session[:attempt_user_updated_at] != user.updated_at.to_s
-      restart_session
-    elsif user.webauthn_enabled? && user_params.key?(:credential) && session[:attempt_user_id]
-      authenticate_with_two_factor_via_webauthn(user)
-    elsif user_params.key?(:otp_attempt) && session[:attempt_user_id]
-      authenticate_with_two_factor_via_otp(user)
-    elsif user.present? && user.external_or_valid_password?(user_params[:password])
-      prompt_for_two_factor(user)
+      if session[:attempt_user_updated_at] != user.updated_at.to_s
+        restart_session
+      elsif user.webauthn_enabled? && user_params.key?(:credential)
+        authenticate_with_two_factor_via_webauthn(user)
+      elsif user_params.key?(:otp_attempt)
+        authenticate_with_two_factor_via_otp(user)
+      end
     end
   end