If we fail to create a cert chain in cms_signeddata_create(), return
KRB5KDC_ERR_PREAUTH_FAILED, which corresponds to a protocol code,
rather than KRB5_PREAUTH_FAILED, which doesn't.  This is also more
consistent with other error clauses in the same function.

ticket: 7718 (new)
target_version: 1.12
tags: pullup

When putting together the set of identity prompts for a responder
challenge, if we don't need a PIN or password of some kind, don't ask
an empty question.

[ghudson@mit.edu: squashed commits, modified commit message, merged
PKCS11 test with current Python script]

Add a password to the set of things that we can pass to a PEM password
callback and the function we use for loading PKCS12 bundles.  If we're
meant to defer identity prompts, just store the name of the identity
which we're loading.  Otherwise, if we're passed a password, use it.
Otherwise, use the prompter callback.

Add a password to the set of things that we can pass to the function
that we use for logging in to PKCS11 tokens, too, but if we're deferring
identity prompts, just return the identity name without doing anything
else.  If not, and we're passed a password, use that.  Otherwise, try to
use the prompter callback to get one.

ticket: 7680

The password callback which we usually supply to NSS already gets a
pointer to the pkinit_identity_crypto_context structure, but it needs to
be passed the name of the identity for which it's being called.

If it gets a name, and it's deferring prompting, just add the identity
to the list of deferred identity prompts (the password callback wouldn't
have been called if its result wasn't needed), and either return NULL
(as an indication that we couldn't get a password) or an empty string (a
value which we know is invalid) if that's handier.

Otherwise, check for a password that's been stashed for its use for that
identity, and return a copy of it if one's found.  If none of that
works, try to use the prompter callback to ask for the password.

ticket: 7680

Use the list of deferred identity prompts and warnings, which we have
after calling pkinit_identity_initialize(), to build a list of questions
to supply to responder callbacks.

Before calling pkinit_identity_prompt() to actually load identities that
are protected, save any passwords and PINs which a responder callback
may have supplied.

Because pkinit_client_prep_questions() can be called multiple times, and
we don't want to try to load all of our identities each of those times,
take some steps to ensure that we only call pkinit_identity_initialize()
and pkinit_identity_prompt() once per request.

ticket: 7680

When called to free identity information, do what the OpenSSL-based
version does, and error out if the identity information is NULL.

Do what the OpenSSL-using code paths do, and load PKCS11_MODNAME if no
module is specified when we're told to use a PKCS11 identity.

Learn to manage a list of deferred identities, for which we want to
prompt for passwords or PINs, in pkinit_identity_crypto_context
structures, along with their associated token flags.  These are opaque
outside of pkinit_crypto_openssl and pkinit_crypto_nss, so both
implementations need to provide wrapper functions that can be called
from elsewhere in the module to populate and query the lists.

ticket: 7680