IdP authentication method selection

[Scott Koranda]

Hello,

The wiki page at

https://wiki.shibboleth.net/confluence/display/SHIB2/IdPUserAuthn

includes this text regarding authentication method selection:

"If the Service Provider does not specify a particular
method, and the user does not have an existing session, then
the default method, identified on the relying party's
configuration, is used. If no default is specified, the IdP
chooses a method randomly."

Is there any information about specifically how the IdP "chooses a method
randomly"? 

I understand that any details are almost certainly subject to
change and should not be relied upon as supported
functionality. The necessary details to configure a
deterministic choice and flow for all situations are well
documented. I am just interested in understanding why a
particular configuration might be functioning the way it is at
this moment.

If this is best answered by examining the code for the IdP I
would be grateful for any hints as to which file and which
lines to consider.

Thanks,

Scott K