When letting users log in we link to the log.in page of the respective wiki.
There is an option to use a warning or error banner above
Unfortunately the styles for [[ https://design.wikimedia.org/style-guide/components/messages.html | notice and success ]]are currently not available here. Also the error and warning messages that are currently available, don't adhere to the current styleguide.
I'm not sure if this is the correct place to file this ticket. This was the best guess of one of our developers at WMDE. Please move it someplace else, if there's a better place for it.
Also pinging @Volker_E since it involves the styleguide.