https/api connection via user and password with api_observer for icinga fails

[tbauriedel]

When you try to enable the foreman-smart-proxy-plugin with api user and password on the foreman server, the connection via https get a bad request and they try to connect again.
(Problem occurs in Icinga 2 version 2.11 and later)
It seems to be a bug in Icinga 2.

Little work around:
If u use the certificates instead of user and password, it works.

I have created an issue on icinga 2: Icinga/icinga2#8213