User authentication with 2 methods

[Björn Urbanek]

Hello!

I have the following setup:
A web application SP and a IdP. Currently all users of the web-app using
there LDAP Login to enter username/password to our IdP (LoginHandler
UsernamePassword).
I want to set up 2 steps:

1.) try to authenticate with the currently to computer logged in user (via
NTLM (?))
2.) If it fails, then use Username/Password login handler, the users have to
enter username/pwd 

What do you think is the best practice for this?

Many thanks!

Bjoern