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Re: [libmicrohttpd] Upgrade to digest authentication


From: DJM-Avalesta
Subject: Re: [libmicrohttpd] Upgrade to digest authentication
Date: Mon, 09 Nov 2020 14:51:17 +0000
User-agent: Roundcube Webmail/1.4-rc2

Many thanks, Christian,

As you say, I had the rnd array allocated on the stack. I moved it to global storage and voila, it works. I should have read the manual more closely.

On the con_cls issue, I guess I'm completing each request so the handler never gets called with a non-zero value.

Best regards

David


On 2020-11-08 5:14 pm, Christian Grothoff wrote:

Hi David,

Looking at the pcap, it seems the 'nonce' of the server keeps changing,
which it must not. I don't know what you are doing, maybe you called
MHD_OPTION_DIGEST_AUTH_RANDOM with a pointer to a location in RAM that
keeps changing.

Anyway, to debug this, I would begin by looking
at the digestauth.c::calculate_nonce() function. Check in particular if
the arguments 'rnd'/rnd_size, or 'uri' or 'realm' change between calls,
they should not (at least not for the same page!).

Again, without reference code from you exhibiting the problematic
behavior, diagnosis help is difficult...

Happy hacking!

-Christian

On 2020-11-07 1:24 pm, DJM-Avalesta wrote:

Hi,

I desperately need to solve issue this for a Client, I attach a wireshark capture of the problem but basically, I have two problems:-

1. Around 50% of the calls to MHD_digest_auth_check() fail returning INVALID_NONCE. This seems to be random, sometimes it passes and sometimes not. Some clients (eg ONVIF Conformance Tool) don't seem to re-send the response with a different nonce when they receive a MHD_queue_auth_fail_response().

2. The *con_cls parameter to the access handler is always null, even though I change it when I get an authentication pass. This means that I'm authenticating every call into the access handler which does not seem right.

I must be doing something wrong as I'm sure this has been tested many times over.

Best regards

David


On 2020-10-31 5:36 pm, Christian Grothoff wrote:

Hi David,

I don't see anything _obviously_ wrong with the snippet you provided. I
would suggest you to use wireshark to log a transcript of the
interaction and/or to provide a stand-alone minimal C implementation
based on your code for testing by others.

Happy hacking!

Christian
 

On 2020-10-29 4:10 pm, DJM-Avalesta wrote:

Hi,

I'm trying to update my 8 year old code to use digest authentication where previously it only supported basic.

I'm trying to use *con_cls (*ptr in my code) to determine when to authenticate but it's not working, *con_cls always seems to be null, even after I've set it, so it's authenticating every time.

I mostly get MHD_digest_auth_check() failures returning INVALID_NONCE and the Client never stops asking for credentials even when the authentication passes, which it does occasionally.

I'm missing something crucial but I can't see it.

The authentication part of my access_handler is shown below

Many thanks

David


static int aptr;
if (bDigestAuth)
{
 printf("URL:%s, con_cls:%p\r\n", url, *ptr);
 //HACK to see if digest authentication works and allows ONVIF snapshorUri test to pass
 //Only works for Admin-Admin
 if (&aptr != *ptr)
 {
  /* Only authenticate on first call of session*/
  char *username;
  const char *password = "Admin";

  g_CameraData->GetRealmName(g_szRealm, sizeof(g_szRealm));

  username = MHD_digest_auth_get_username(connection);
  if (username == NULL)
  {
    response = MHD_create_response_from_data (strlen (NOTAUTH_RESPONSE),
    (void *) NOTAUTH_RESPONSE,
    MHD_NO, MHD_NO);
    ret = MHD_queue_auth_fail_response(connection, g_szRealm,
      OPAQUE,
      response,
      MHD_NO);
    MHD_destroy_response(response);
    pthread_mutex_unlock (&m_AuthMutex); //unlock after authorization
    // printf("Failed digest auth, no username\r\n");
    return ret;
  }
  printf("Applying digest auth to user: %s, realm:%s, con_cls:%p\r\n", username, g_szRealm, *ptr);
  *ptr = &aptr; //set this for session
  ret = MHD_digest_auth_check(connection, g_szRealm,
    username,
    password,
    300);
  printf("Checking digest auth for username: %s, password: %s, realm:%s\r\n", username, password, g_szRealm);
  free(username);
  if ( (ret == MHD_INVALID_NONCE) ||
    (ret == MHD_NO) )
  {
    printf("Failed digest auth, invalid nonce, ret:%d\r\n", ret);
    response = MHD_create_response_from_data (strlen (NOTAUTH_RESPONSE),
      (void *) NOTAUTH_RESPONSE,
      MHD_NO, MHD_NO);
    if (NULL == response)
      return MHD_NO;
    ret = MHD_queue_auth_fail_response(connection, g_szRealm,
      OPAQUE,
      response,
      (ret == MHD_INVALID_NONCE) ? MHD_YES : MHD_NO);
    MHD_destroy_response(response);
    pthread_mutex_unlock (&m_AuthMutex); //unlock after authorization
    return ret;
  }
  //PASSED
  printf("PASSED digest auth\r\n");
 }
 else
 {
   printf("No digest auth required\r\n");
 }
}


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