Migrate all the logging handlers to namespaces. Make SimpleSAML\Logger a bit more intelligent so that it allows using custom logging handlers. Now you just need to implement SimpleSAML\Logger\LogginghandlerInterface in a class, and set the 'logging.handler' option in the configuration file to a string with the full name of your class.

Fix build. If we are logging to STDERR, we don't have to write to the filesystem anyway, so why checking?