Partially revert 4466fcf1bc.

lib/auth/default_current_user_provider.rb

@@ -25,7 +25,6 @@ class Auth::DefaultCurrentUserProvider
   # our current user, return nil if none is found
   def current_user
     return @env[CURRENT_USER_KEY] if @env.key?(CURRENT_USER_KEY)
-    raise Discourse::ReadOnly if Discourse.pg_readonly_mode?
 
     # bypass if we have the shared session header
     if shared_key = @env['HTTP_X_SHARED_SESSION_KEY']