better logs when an error happens in SSO

app/controllers/session_controller.rb

@@ -117,7 +117,14 @@ class SessionController < ApplicationController
       SingleSignOn::ACCESSORS.each do |a|
         details[a] = sso.send(a)
       end
-      Rails.logger.error "Failed to create or lookup user: #{e}\n\n#{details.map{|k,v| "#{k}: #{v}"}.join("\n")}"
+
+      message = "Failed to create or lookup user: #{e}."
+      message << "\n\n" << "-" * 100
+      message << details.map { |k,v| "#{k}: #{v}" }.join("\n")
+      message << "\n\n" << "-" * 100
+      message << e.backtrace.join("\n")
+
+      Rails.logger.error(message)
 
       render text: I18n.t("sso.unknown_error"), status: 500
     end

app/models/discourse_single_sign_on.rb

@@ -81,19 +81,21 @@ class DiscourseSingleSignOn < SingleSignOn
   private
 
   def match_email_or_create_user(ip_address)
-    user = User.find_by_email(email)
+    unless user = User.find_by_email(email)
+      try_name = name.presence
+      try_username = username.presence
 
-    try_name = name.blank? ? nil : name
-    try_username = username.blank? ? nil : username
+      user_params = {
+        email: email,
+        name: try_name || User.suggest_name(try_username || email),
+        username: UserNameSuggester.suggest(try_username || try_name || email),
+        ip_address: ip_address
+      }
 
-    user_params = {
-      email: email,
-      name:  try_name || User.suggest_name(try_username || email),
-      username: UserNameSuggester.suggest(try_username || try_name || email),
-      ip_address: ip_address
-    }
+      user = User.create!(user_params)
+    end
 
-    if user || user = User.create!(user_params)
+    if user
       if sso_record = user.single_sign_on_record
         sso_record.last_payload = unsigned_payload
         sso_record.external_id = external_id