Trying to find a portable way to get the active Kerberos principal name

gss-test.c

#include <stdio.h>
#ifdef __APPLE__
  /* /System/Library/Frameworks/GSS.framework/GSS should be statically linked */
  #include <GSS/GSS.h>
#else
  #include <gssapi/gssapi.h>
  #include <gssapi/gssapi_krb5.h>
#endif


void init_gss() {
  OM_uint32 major_status, minor_status;

  /* gss_init_sec_context(&minor_status, */

}

void acquire_cred() {
  gss_cred_id_t cred = NULL;
  OM_uint32 minor_status;

  gss_name_t aname = NULL;

}

char * display_name(gss_name_t name, gss_buffer_t str) {
  OM_uint32 minor_status;
  gss_OID type;

  gss_display_name(&minor_status, name, str, &type);

  return str->value;
}

void inquire_cred() {
  OM_uint32 minor_status;

  gss_name_t name;
  OM_uint32 lifetime;
  gss_buffer_desc str;

  int rv = gss_inquire_cred(&minor_status, GSS_C_NO_CREDENTIAL, &name, &lifetime, NULL, NULL);

  switch(rv) {
    case GSS_S_COMPLETE:
      printf("%s valid for %d seconds\n", display_name(name, &str), lifetime);
      break;
    case GSS_S_CREDENTIALS_EXPIRED:
      printf("%s is expired\n", display_name(name, &str));
      break;
    case GSS_S_DEFECTIVE_CREDENTIAL:
      printf("%s is not valid\n", display_name(name, &str));
      break;
    case GSS_S_NO_CRED:
      puts("There are no default credentials available.");
      break;
    default:
      printf("Something bad happened: minor status %d\n", minor_status);
      break;
  }
}


int main() {
  inquire_cred();
}

gss.rb

require 'ffi'

module GSS
  extend FFI::Library
  FFI::add_typedef(:uint32, :OM_uint32)

  ffi_lib ['/System/Frameworks/GSS.framework/GSS', 'gss'], FFI::Library::LIBC

  # void *malloc(size_t size);
  attach_function :malloc, [:size_t], :pointer

  # void *memcpy(void *dest, const void *src, size_t n);
  attach_function :memcpy, [:pointer, :pointer, :size_t], :pointer

  # OM_uint32 gss_display_name(OM_uint32 *  minor_status,
  #                              gss_name_t input_name,
  #                              gss_buffer_t output_name_buffer,
  #                              gss_OID *  output_name_type)
  attach_function :gss_display_name, [:pointer, :pointer, :pointer, :pointer], :OM_uint32

  # OM_uint32 gss_inquire_cred(OM_uint32 *        minor_status,
  #                             gss_cred_id_t      cred_handle,
  #                             gss_name_t *       name,
  #                             OM_uint32 *        lifetime,
  #                             gss_cred_usage_t * cred_usage,
  #                             gss_OID_set *      mechanisms)
  attach_function :gss_inquire_cred, 6.times.collect { :pointer }, :OM_uint32

  # OM_uint32 gss_release_name(OM_uint32 * minor_status, gss_name_t * name);
  attach_function :gss_release_name, [:pointer, :pointer], :OM_uint32

  # OM_uint32 gss_release_buffer(OM_uint32 * minor_status, gss_buffer_t buffer);
  attach_function :gss_release_buffer, [:pointer, :pointer], :OM_uint32

  # OM_uint32 gss_release_cred(OM_uint32 *minor_status, gss_cred_id_t *cred_handle);
  attach_function :gss_release_cred, [:pointer, :pointer], :OM_uint32

end