UI - add strong auth (non-pwd based)

[tpurschke]

• 2-factor auth with certificates to (web based) client
• optionally allow admin to activate 2FA

[tpurschke]

Also think about

• latest development regarding passkeys (https://support.google.com/accounts/answer/13548313?hl=en) or
• add Azure support for user authentication (in addition to LDAP auth servers, have a look at authentication mode (OAUTH) used in Azure, see https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/auth-oauth2)