GUACAMOLE-2057: Add configuration parameters for supporting Kerberos authentication for RDP.

[necouchman]

Adds the required parameters to configure the FreeRDP library to force Kerberos and configure a couple of the parameters related to that, if required. I have tested the changes against both servers with NTLM still enabled and against one where NTLM is disabled, and it seems to work, but others should feel free to test.

I do need one bit of help with this - I have not added the detection of the Kerberos support to the configure.ac file, yet, as I'm struggling to figure out how to do that. In my mind, it needs 2-3 checks:

• Check if FreeRDP contains support for the FreeRDP_AuthenticationPackageList setting. This is probably the biggest thing I'm struggling with, as this setting is part of an enum in one of the FreeRDP header files, but I'm having trouble finding any guidance on how to generate an autoconf check for an enum member? Any hints on the best way to do that would be appreciated.
• Check if FreeRDP is built with Kerberos support. There's a flag in the FreeRDP buildconfig.h file, within the constant FREERDP_BUILD_CONFIG that shows WITH_KRB5=ON, but, again, I'm struggling with how to get autoconf to check for this, or identify a sane method or member to use with one of the other autoconf checks.

[jbostoen]

Just a typo (NTML > NTLM)

[corentin-soriano]

The specific Kerberos code should only be enabled with FreeRDP >= 3.x to avoid compilation errors in 2.x.

[mike-jumper]

It doesn't look to me like the path is evaluated relative to GUACAMOLE_HOME, but passed to FreeRDP unaltered (and then interpreted by FreeRDP relative to somewhere?).

[mike-jumper]

Should this be part of the security parameter, rather than separate?

[corentin-soriano]

These are two different parameters. We may need to choose an explicit value for each

[corentin-soriano]

• Check if FreeRDP contains support for the FreeRDP_AuthenticationPackageList setting. This is probably the biggest thing I'm struggling with, as this setting is part of an enum in one of the FreeRDP header files, but I'm having trouble finding any guidance on how to generate an autoconf check for an enum member? Any hints on the best way to do that would be appreciated.

This test seems to work:

if test "x${have_freerdp}" = "xyes"
then
    AC_CHECK_DECL([FreeRDP_AuthenticationPackageList],
                  [AC_DEFINE([HAVE_FREERDP_AUTHENTICATION_PACKAGE_LIST],,
                             [Defined if FreeRDP_AuthenticationPackageList is available])],,
                  [#include <freerdp/settings.h>])
fi

However, FreeRDP_AuthenticationPackageList seems to have been added for version 3.0.0 so I'm not sure if it's necessary to check it.

What needs to be removed are these assignments when not HAVE_SETTERS_GETTERS (freerdp 2.x):

rdp_settings->AuthenticationPackageList
rdp_settings->KerberosKdcUrl
rdp_settings->KerberosCache

settings.c: In function ‘guac_rdp_push_settings’:
settings.c:2019:25: error: ‘rdpSettings’ {aka ‘struct rdp_settings’} has no member named ‘AuthenticationPackageList’
 2019 |             rdp_settings->AuthenticationPackageList = "ntlm,!kerberos";
      |                         ^~
settings.c:2023:25: error: ‘rdpSettings’ {aka ‘struct rdp_settings’} has no member named ‘AuthenticationPackageList’
 2023 |             rdp_settings->AuthenticationPackageList = "!ntlm,kerberos";
      |                         ^~
settings.c:2027:25: error: ‘rdpSettings’ {aka ‘struct rdp_settings’} has no member named ‘AuthenticationPackageList’
 2027 |             rdp_settings->AuthenticationPackageList = "ntlm,kerberos";
      |                         ^~
settings.c:2033:19: error: ‘rdpSettings’ {aka ‘struct rdp_settings’} has no member named ‘KerberosKdcUrl’; did you mean ‘KerberosKdc’?
 2033 |     rdp_settings->KerberosKdcUrl = guac_strdup(guac_settings->kdc_url);
      |                   ^~~~~~~~~~~~~~
      |                   KerberosKdc
settings.c:2036:19: error: ‘rdpSettings’ {aka ‘struct rdp_settings’} has no member named ‘KerberosCache’; did you mean ‘KerberosKdc’?
 2036 |     rdp_settings->KerberosCache = guac_strdup(guac_settings->kerberos_cache);
      |                   ^~~~~~~~~~~~~
      |                   KerberosKdc
make[4]: *** [Makefile:1370: libguac_client_rdp_la-settings.lo] Error 1