FIDO2: support pin-less LUKS enroll/unlock

Closes: https://github.com/systemd/systemd/issues/19246

Some FIDO2 devices allow the user to choose whether to use a PIN or not
and will HMAC with a different secret depending on the choice.
Some other devices (or some device-specific configuration) can instead
make it mandatory.
Allow the cryptenroll user to choose whether to use a PIN or not, but
fail immediately if it is a hard requirement.
Record the choice in the JSON-encoded LUKS header metadata so that the
right set of options can be used on unlock.

src/cryptsetup/cryptsetup.c

@@ -739,6 +739,7 @@ static int attach_luks_or_plain_or_bitlk_by_fido2(
         int keyslot = arg_key_slot, r;
         const char *rp_id;
         const void *cid;
+        Fido2EnrollFlags required;
 
         assert(cd);
         assert(name);
@@ -759,7 +760,8 @@ static int attach_luks_or_plain_or_bitlk_by_fido2(
                                 &discovered_salt_size,
                                 &discovered_cid,
                                 &discovered_cid_size,
-                                &keyslot);
+                                &keyslot,
+                                &required);
 
                 if (IN_SET(r, -ENOTUNIQ, -ENXIO))
                         return log_debug_errno(SYNTHETIC_ERRNO(EAGAIN),
@@ -767,6 +769,10 @@ static int attach_luks_or_plain_or_bitlk_by_fido2(
                 if (r < 0)
                         return r;
 
+                if (FLAGS_SET(required, FIDO2ENROLL_PIN) && arg_headless)
+                        return log_error_errno(SYNTHETIC_ERRNO(ENOPKG),
+                                               "A PIN is required to unlock this volume, but the 'headless' parameter was set.");
+
                 rp_id = discovered_rp_id;
                 key_data = discovered_salt;
                 key_data_size = discovered_salt_size;
@@ -791,6 +797,7 @@ static int attach_luks_or_plain_or_bitlk_by_fido2(
                                 key_data, key_data_size,
                                 until,
                                 arg_headless,
+                                required,
                                 &decrypted_key, &decrypted_key_size);
                 if (r >= 0)
                         break;