psk: Add basic support for RFC 9258 external PSK importer interface

This adds a minimal, callback-based API to import external PSK,
following RFC 9258.  The client and the server importing external PSK
are supposed to set a callback to retrieve PSK, which returns flags
that may indicate the PSK is imported, along with the key:

  typedef int gnutls_psk_client_credentials_function3(
          gnutls_session_t session,
          gnutls_datum_t *username, gnutls_datum_t *key,
          gnutls_psk_key_flags *flags);

  typedef int gnutls_psk_server_credentials_function3(
          gnutls_session_t session,
          const gnutls_datum_t *username, gnutls_datum_t *key,
          gnutls_psk_key_flags *flags);

Those callbacks are responsible to call
gnutls_psk_format_imported_identity() for external PSKs to build a
serialized PSK identity, and set GNUTLS_PSK_KEY_EXT in flags if the
identity is an imported one.

Signed-off-by: Daiki Ueno <ueno@gnu.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/handshake-defs.h b/lib/handshake-defs.h
index 1b0c250e75..51aa5d2369 100644
--- a/lib/handshake-defs.h
+++ b/lib/handshake-defs.h
@@ -25,10 +25,12 @@
 #define EARLY_TRAFFIC_LABEL "c e traffic"
 #define EXT_BINDER_LABEL "ext binder"
 #define RES_BINDER_LABEL "res binder"
+#define IMP_BINDER_LABEL "imp binder"
 #define EARLY_EXPORTER_MASTER_LABEL "e exp master"
 #define HANDSHAKE_CLIENT_TRAFFIC_LABEL "c hs traffic"
 #define HANDSHAKE_SERVER_TRAFFIC_LABEL "s hs traffic"
 #define DERIVED_LABEL "derived"
+#define DERIVED_PSK_LABEL "derived psk"
 #define APPLICATION_CLIENT_TRAFFIC_LABEL "c ap traffic"
 #define APPLICATION_SERVER_TRAFFIC_LABEL "s ap traffic"
 #define APPLICATION_TRAFFIC_UPDATE "traffic upd"