Userauth none bypasses wolfSSHd credential check

When wolfsshd is built with WOLFSSH_ALLOW_USERAUTH_NONE, the
DefaultUserAuth() function accepted WOLFSSH_USERAUTH_NONE as a valid
auth type and forwarded it to RequestAuthentication(). Since
RequestAuthentication() only gates credential checks on PASSWORD and
PUBLICKEY types, a none request for any existing system user returned
success without verifying any credential. Removed USERAUTH_NONE as an
accepted auth type in DefaultUserAuth() so it is treated as an invalid
auth type for wolfsshd.

Affected function: DefaultUserAuth.
Issue: F-3215

Author: ejohnstown

apps/wolfsshd/auth.c

@@ -1078,8 +1078,11 @@ static int DoCheckUser(const char* usr, WOLFSSHD_AUTH* auth)
 }
 
 
-/* @TODO this will take in a pipe or equivalent to talk to a privileged thread
- * rather than having WOLFSSHD_AUTH directly with privilege separation */
+/*
+ * @TODO this will take a pipe or equivalent to talk to a privileged thread
+ * rather than having WOLFSSHD_AUTH directly with privilege separation.
+ * Note: authData->type of WOLFSSH_USERAUTH_NONE is not valid for wolfsshd.
+ */
 static int RequestAuthentication(WS_UserAuthData* authData,
                                  WOLFSSHD_AUTH* authCtx)
 {
@@ -1091,6 +1094,12 @@ static int RequestAuthentication(WS_UserAuthData* authData,
         return WOLFSSH_USERAUTH_FAILURE;
     }
 
+    if (authData->type == WOLFSSH_USERAUTH_NONE) {
+        wolfSSH_Log(WS_LOG_ERROR,
+                "[SSHD] Auth type NONE invalid.");
+        return WOLFSSH_USERAUTH_INVALID_AUTHTYPE;
+    }
+
     usr = (const char*)authData->username;
     ret = DoCheckUser(usr, authCtx);
     /* temporarily elevate permissions */
@@ -1291,9 +1300,6 @@ int DefaultUserAuth(byte authType, WS_UserAuthData* authData, void* ctx)
     }
 
     if (authType != WOLFSSH_USERAUTH_PASSWORD &&
-#ifdef WOLFSSH_ALLOW_USERAUTH_NONE
-        authType != WOLFSSH_USERAUTH_NONE &&
-#endif
         authType != WOLFSSH_USERAUTH_PUBLICKEY) {
 
         ret = WOLFSSH_USERAUTH_INVALID_AUTHTYPE;