[Openvpn-devel,v3,3/5] Implement sending response to challenge via CR_RESPONSE

diff --git a/doc/management-notes.txt b/doc/management-notes.txt
index e54e1082..a7ae84e3 100644
--- a/doc/management-notes.txt
+++ b/doc/management-notes.txt
@@ -806,6 +806,20 @@  To accept connecting to the host and port directly, use this command:
 
   proxy NONE
 
+COMMAND -- cr-response (OpenVPN 2.5 or higher)
+-------------------------------------------------
+Provides support for sending responses a challenge/response
+query via INFOMSG,CR_TEXT. The response should be base64 encoded:
+
+  cr-response SGFsbG8gV2VsdCE=
+
+The document is intended to be used after the client received a
+CR_TEXT challenge (see send-pending-auth section). The answer is
+the answer to the challenge and depends on the challenge itself
+for a TOTP challenge this would the number encoded as base64 or
+just a string for a challenge like what "day is it today?".
+
+
 COMMAND -- pk-sig (OpenVPN 2.5 or higher, management version > 1)
 COMMAND -- rsa-sig (OpenVPN 2.3 or higher, management version <= 1)
 -----------------------------------------------------------------
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 70cd493a..2c8db68d 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -291,6 +291,44 @@  ce_management_query_proxy(struct context *c)
     return ret;
 }
 
+/**
+ * This method sends a custom control channel message
+ *
+ * This will write the control message
+ *
+ *  command parm1,parm2,..
+ *  .
+ * to the control channel.
+ *
+ * @param arg           The context struct
+ * @param command       The command being sent
+ * @param parameters    the parameters to the command
+ * @return              if sending was successful
+ */
+static bool
+management_callback_send_cc_message(void *arg,
+                                    const char *command,
+                                    const char *parameters)
+{
+    struct context *c = (struct context *) arg;
+    size_t len = strlen(command) + 1 + sizeof(parameters) + 1;
+    if (len > PUSH_BUNDLE_SIZE)
+    {
+        return false;
+    }
+
+    struct gc_arena gc = gc_new();
+    struct buffer buf = alloc_buf_gc(len, &gc);
+    ASSERT(buf_printf(&buf, "%s", command));
+    if (parameters)
+    {
+        ASSERT(buf_printf(&buf, ",%s", parameters));
+    }
+    bool status = send_control_channel_string(c, BSTR(&buf), D_PUSH);
+
+    gc_free(&gc);
+    return status;
+}
 
 static bool
 management_callback_remote_cmd(void *arg, const char **p)
@@ -3973,6 +4011,7 @@  init_management_callback_p2p(struct context *c)
         cb.show_net = management_show_net_callback;
         cb.proxy_cmd = management_callback_proxy_cmd;
         cb.remote_cmd = management_callback_remote_cmd;
+        cb.send_cc_message = management_callback_send_cc_message;
 #ifdef TARGET_ANDROID
         cb.network_change = management_callback_network_change;
 #endif
diff --git a/src/openvpn/manage.c b/src/openvpn/manage.c
index 195941ca..a72c7678 100644
--- a/src/openvpn/manage.c
+++ b/src/openvpn/manage.c
@@ -75,6 +75,7 @@  man_help(void)
     msg(M_CLIENT, "auth-retry t           : Auth failure retry mode (none,interact,nointeract).");
     msg(M_CLIENT, "bytecount n            : Show bytes in/out, update every n secs (0=off).");
     msg(M_CLIENT, "echo [on|off] [N|all]  : Like log, but only show messages in echo buffer.");
+    msg(M_CLIENT, "cr-response response   : Send a challenge response answer via CR_RESPONSE to server");
     msg(M_CLIENT, "exit|quit              : Close management session.");
     msg(M_CLIENT, "forget-passwords       : Forget passwords entered so far.");
     msg(M_CLIENT, "help                   : Print this message.");
@@ -779,6 +780,27 @@  man_net(struct management *man)
     }
 }
 
+static void
+man_send_cc_message(struct management *man, const char *message, const char *parameters)
+{
+    if (man->persist.callback.send_cc_message)
+    {
+        const bool status = (*man->persist.callback.send_cc_message)
+                                (man->persist.callback.arg, message, parameters);
+        if (status)
+        {
+            msg(M_CLIENT, "SUCCESS: command succeeded");
+        }
+        else
+        {
+            msg(M_CLIENT, "ERROR: command failed");
+        }
+    }
+    else
+    {
+        msg(M_CLIENT, "ERROR: This command is not supported by the current daemon mode");
+    }
+}
 #ifdef ENABLE_PKCS11
 
 static void
@@ -1144,7 +1166,15 @@  man_load_stats(struct management *man)
 }
 
 #define MN_AT_LEAST (1<<0)
-
+/**
+ * Checks if the correct number of arguments to a management command are present
+ * and otherwise prints an error and returns false.
+ *
+ * @param p         pointer to the parameter array
+ * @param n         number of arguments required
+ * @param flags     if MN_AT_LEAST require at least n parameters and not exactly n
+ * @return          Return whether p has n (or at least n) parameters
+ */
 static bool
 man_need(struct management *man, const char **p, const int n, unsigned int flags)
 {
@@ -1460,6 +1490,13 @@  man_dispatch_command(struct management *man, struct status_output *so, const cha
             man_query_need_str(man, p[1], p[2]);
         }
     }
+    else if (streq(p[0], "cr-response"))
+    {
+        if (man_need(man, p, 1, 0))
+        {
+            man_send_cc_message(man, "CR_RESPONSE", p[1]);
+        }
+    }
     else if (streq(p[0], "net"))
     {
         man_net(man);
diff --git a/src/openvpn/manage.h b/src/openvpn/manage.h
index 6f5f34c1..e1dabceb 100644
--- a/src/openvpn/manage.h
+++ b/src/openvpn/manage.h
@@ -164,6 +164,7 @@  struct management_callback
     int (*kill_by_addr) (void *arg, const in_addr_t addr, const int port);
     void (*delete_event) (void *arg, event_t event);
     int (*n_clients) (void *arg);
+    bool (*send_cc_message) (void *arg, const char *message, const char *parameter);
 #ifdef MANAGEMENT_DEF_AUTH
     bool (*kill_by_cid)(void *arg, const unsigned long cid, const char *kill_msg);
     bool (*client_auth) (void *arg,