HTTPURLSession digest authentication using HA1 (not password)

Question

I just have a scenario in which digest authentication is performed using the user name and HA1 values ​​(which was calculated somewhere in the past or it was a provider by authenticating on another server). Password is not available.

Now, how do I handle this script using NSURLSession ?

Do I need to do this manually (calculate HA2 and my response ) or is there some solution for this? (it should be there, since saving the password, as plain text is a security issue).

Note that I have a scenario in which HA1 comes from authentication on another server, so NSURLCredential persistence with a value of NSURLCredentialPersistencePermanent does not solve my problem.