DEV: reduce logging when no external id is specified

Previously we were returning an unknown sso error and logging a message
when external id was blank. This noise is not needed.

spec/rails_helper.rb

@@ -385,3 +385,26 @@ def silence_stdout
 ensure
   STDOUT.unstub(:write)
 end
+
+class TrackingLogger < ::Logger
+  attr_reader :messages
+  def initialize(level: nil)
+    super(nil)
+    @messages = []
+    @level = level
+  end
+  def add(*args, &block)
+    if !level || args[0].to_i >= level
+      @messages << args
+    end
+  end
+end
+
+def track_log_messages(level: nil)
+  old_logger = Rails.logger
+  logger = Rails.logger = TrackingLogger.new(level: level)
+  yield logger.messages
+  logger.messages
+ensure
+  Rails.logger = old_logger
+end