modeled like our other section config api calls
two drawbacks of doing it this way:
* we have to copy some api properties again for the update call,
since not all of them are updateable (username-claim)
* we only handle openid for now, which we would have to change
when we add ldap/ad
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>