Can't login with user with umlauts in username and password

What are the steps to reproduce your problem?
Add a user with userId 'sören' and password 'sören'.
Add user sören to group camunda-admin

What is the problem?
sören cannot login to camunda webapp. message: Login Failed :
Wrong credentials or missing access rights to application

What would be the expected behavior:
sören can access all applications,

Hints (optional):
Encoded data from the login request: username:s%C3%B6ren
password:s%C3%B6ren