Add extern apis mbedtls_ticket_get_psk.

Signed-off-by: Xiaokang Qian <xiaokang.qian@arm.com>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 513937e..3de164c 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1574,4 +1574,31 @@
     return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
 }
 
+#ifdef MBEDTLS_SSL_SESSION_TICKETS
+int mbedtls_ssl_tls13_ticket_get_psk(mbedtls_ssl_context *ssl,
+                                     psa_algorithm_t *hash_alg,
+                                     const unsigned char **psk,
+                                     size_t *psk_len)
+{
+
+    mbedtls_ssl_session *session = ssl->session_negotiate;
+    const mbedtls_ssl_ciphersuite_t *ciphersuite_info = NULL;
+
+    if (ssl->handshake->resume == 0 || session == NULL ||
+        session->ticket == NULL) {
+        return -1;
+    }
+
+    ciphersuite_info = mbedtls_ssl_ciphersuite_from_id(session->ciphersuite);
+    if (ciphersuite_info != NULL) {
+        *hash_alg = mbedtls_psa_translate_md(ciphersuite_info->mac);
+    }
+
+    *psk = session->resumption_key;
+    *psk_len = session->resumption_key_len;
+
+    return 0;
+}
+#endif /* MBEDTLS_SSL_SESSION_TICKETS */
+
 #endif /* MBEDTLS_SSL_TLS_C && MBEDTLS_SSL_PROTO_TLS1_3 */