Add option to enforce usage of SCRAM-*-PLUS variants

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

src/auth.c

@@ -799,7 +799,9 @@ static void _auth(xmpp_conn_t *conn)
             conn->ctx, "auth",
             "Password hasn't been set, and SASL ANONYMOUS unsupported.");
         xmpp_disconnect(conn);
-    } else if (conn->sasl_support & SASL_MASK_SCRAM) {
+    } else if ((conn->sasl_support & SASL_MASK_SCRAM_PLUS) ||
+               ((conn->sasl_support & SASL_MASK_SCRAM_WEAK) &&
+                !conn->only_strong_auth)) {
         size_t n;
         scram_ctx = strophe_alloc(conn->ctx, sizeof(*scram_ctx));
         memset(scram_ctx, 0, sizeof(*scram_ctx));
@@ -857,7 +859,8 @@ static void _auth(xmpp_conn_t *conn)
 
         /* SASL algorithm was tried, unset flag */
         conn->sasl_support &= ~scram_ctx->alg->mask;
-    } else if (conn->sasl_support & SASL_MASK_DIGESTMD5) {
+    } else if ((conn->sasl_support & SASL_MASK_DIGESTMD5) &&
+               conn->weak_auth_enabled) {
         auth = _make_sasl_auth(conn, "DIGEST-MD5");
         if (!auth) {
             disconnect_mem_error(conn);
@@ -871,7 +874,8 @@ static void _auth(xmpp_conn_t *conn)
 
         /* SASL DIGEST-MD5 was tried, unset flag */
         conn->sasl_support &= ~SASL_MASK_DIGESTMD5;
-    } else if (conn->sasl_support & SASL_MASK_PLAIN) {
+    } else if ((conn->sasl_support & SASL_MASK_PLAIN) &&
+               conn->weak_auth_enabled) {
         auth = _make_sasl_auth(conn, "PLAIN");
         if (!auth) {
             disconnect_mem_error(conn);

src/common.h

@@ -259,6 +259,8 @@ struct _xmpp_conn_t {
     int sasl_support; /* if true, field is a bitfield of supported
                          mechanisms */
     int auth_legacy_enabled;
+    int weak_auth_enabled;
+    int only_strong_auth;
     int secured; /* set when stream is secured with TLS */
     xmpp_certfail_handler certfail_handler;
     xmpp_password_callback password_callback;

src/conn.c

@@ -1133,6 +1133,8 @@ long xmpp_conn_get_flags(const xmpp_conn_t *conn)
         XMPP_CONN_FLAG_DISABLE_SM * conn->sm_disable |
         XMPP_CONN_FLAG_ENABLE_COMPRESSION * conn->compression.allowed |
         XMPP_CONN_FLAG_COMPRESSION_DONT_RESET * conn->compression.dont_reset |
+        XMPP_CONN_FLAG_WEAK_AUTH * conn->weak_auth_enabled |
+        XMPP_CONN_FLAG_STRONG_AUTH * conn->only_strong_auth |
         XMPP_CONN_FLAG_LEGACY_AUTH * conn->auth_legacy_enabled;
 
     return flags;
@@ -1188,11 +1190,14 @@ int xmpp_conn_set_flags(xmpp_conn_t *conn, long flags)
         (flags & XMPP_CONN_FLAG_ENABLE_COMPRESSION) ? 1 : 0;
     conn->compression.dont_reset =
         (flags & XMPP_CONN_FLAG_COMPRESSION_DONT_RESET) ? 1 : 0;
+    conn->weak_auth_enabled = (flags & XMPP_CONN_FLAG_WEAK_AUTH) ? 1 : 0;
+    conn->only_strong_auth = (flags & XMPP_CONN_FLAG_STRONG_AUTH) ? 1 : 0;
     flags &= ~(XMPP_CONN_FLAG_DISABLE_TLS | XMPP_CONN_FLAG_MANDATORY_TLS |
                XMPP_CONN_FLAG_LEGACY_SSL | XMPP_CONN_FLAG_TRUST_TLS |
                XMPP_CONN_FLAG_LEGACY_AUTH | XMPP_CONN_FLAG_DISABLE_SM |
                XMPP_CONN_FLAG_ENABLE_COMPRESSION |
-               XMPP_CONN_FLAG_COMPRESSION_DONT_RESET);
+               XMPP_CONN_FLAG_COMPRESSION_DONT_RESET |
+               XMPP_CONN_FLAG_WEAK_AUTH | XMPP_CONN_FLAG_STRONG_AUTH);
     if (flags) {
         strophe_error(conn->ctx, "conn", "Flags 0x%04lx unknown", flags);
         return XMPP_EINVOP;

strophe.h

@@ -208,6 +208,14 @@ typedef struct _xmpp_sm_t xmpp_sm_state_t;
  *  Only enable this flag if you know what you're doing.
  */
 #define XMPP_CONN_FLAG_COMPRESSION_DONT_RESET (1UL << 7)
+/** @def XMPP_CONN_FLAG_WEAK_AUTH
+ *  Allow weak authentication methods (DIGEST-MD5 and PLAIN).
+ */
+#define XMPP_CONN_FLAG_WEAK_AUTH (1UL << 8)
+/** @def XMPP_CONN_FLAG_STRONG_AUTH
+ *  Only allow strong authentication methods (Only the SCRAM-*-PLUS variants).
+ */
+#define XMPP_CONN_FLAG_STRONG_AUTH (1UL << 9)
 
 /* connect callback */
 typedef enum {