v0.5 -- change of approach given Discourse changes -- the Auth::DefaultCurrentUserProvider class has a current_user method which we want to try extending instead.

plugin.rb

@@ -4,57 +4,57 @@
 
 # name: discourse-md5_authentication
 # about: A plugin to authenticate users with MD5 passwords from legacy systems
-# version: 0.4
+# version: 0.5
 # authors: saint
 # url: https://gitea.federated.computer/saint/discourse-md5_authentication.git
 
-# This block of code is executed after the Discourse application is initialized.
+# This block will run after Discourse has initialized
 after_initialize do
-  # Reopening the Auth::DefaultAuthenticator class to add custom authentication logic.
-  class ::Auth::DefaultAuthenticator
-    # Define a module to encapsulate the MD5 authentication logic.
-    module LegacyMd5Authentication
-      # This method is called when the module is prepended to the class.
-      # It creates an alias for the existing authenticate method to preserve it.
-      def self.prepended(base)
-        base.singleton_class.class_eval do
-          alias_method :old_authenticate, :authenticate
-        end
-      end
+  # Define a module to contain the MD5 authentication logic
+  module LegacyMd5Authentication
+    # Override the current_user method to include MD5 authentication
+    def current_user
+      # Attempt to find the current user using the standard Discourse method
+      user = super
+      return user if user
 
-      # Override the authenticate method to add custom MD5 password logic.
-      def authenticate(email_or_username, password)
-        # Log an attempt to authenticate.
+      # Check for MD5 authentication if no user is found by the standard method
+      email_or_username = @request.params[:login]
+      password = @request.params[:password]
+
+      if email_or_username && password
+        # Log the start of the MD5 authentication attempt
         Rails.logger.info("MD5 Auth: Attempting to authenticate #{email_or_username}")
 
-        # Find the user by their username or email.
+        # Find the user by username or email, ignoring case
         user = User.find_by_username_or_email(email_or_username.downcase.strip)
 
-        # Log if a user is found.
-        if user
-          Rails.logger.info("MD5 Auth: User found - #{user.username}")
+        # Log if a user with an MD5 password is found
+        if user && user.custom_fields['md5_password']
+          Rails.logger.info("MD5 Auth: User found with MD5 password - #{user.username}")
+
+          # Check if the provided password matches the stored MD5 password
+          if user.custom_fields['md5_password'] == Digest::MD5.hexdigest(password)
+            # Log the successful MD5 password match
+            Rails.logger.info("MD5 Auth: MD5 password match for user #{user.username}")
+
+            # Update the user to use the new password and clear the MD5 password
+            user.update!(password: password)
+            user.custom_fields['md5_password'] = nil
+            user.save_custom_fields
+
+            # Set the current user in the environment
+            @env[CURRENT_USER_KEY] = user
+            return user
+          end
         end
-
-        # Check if the user's custom field contains an MD5 password and if it matches the provided password.
-        if user && user.custom_fields['md5_password'] && user.custom_fields['md5_password'] == Digest::MD5.hexdigest(password)
-          Rails.logger.info("MD5 Auth: MD5 password match for user #{user.username}")
-          
-          # Update the user's password to the new format and clear the MD5 password field.
-          user.update!(password: password)
-          user.custom_fields['md5_password'] = nil
-          user.save_custom_fields
-
-          # Return an authentication result indicating success.
-          return Auth::Result.new(user)
-        end
-
-        # If MD5 authentication fails, fall back to the original authentication method.
-        Rails.logger.info("MD5 Auth: Falling back to default authentication for #{email_or_username}")
-        old_authenticate(email_or_username, password)
       end
-    end
 
-    # Prepend the module to the DefaultAuthenticator class.
-    prepend LegacyMd5Authentication
+      # Fallback to the original current_user method
+      nil
+    end
   end
+
+  # Prepend our module to the DefaultCurrentUserProvider class
+  Auth::DefaultCurrentUserProvider.prepend LegacyMd5Authentication
 end