Remove krb5_get_max_time_skew portability hack (#1875)

This function has been available in Kerberos libraries
for over ten years now.

acinclude/krb5.m4

@@ -105,23 +105,6 @@ main(void)
   SQUID_DEFINE_BOOL(HAVE_BROKEN_HEIMDAL_KRB5_H,$squid_cv_broken_heimdal_krb5_h,[Heimdal krb5.h is broken for C++])
 ]) dnl SQUID_CHECK_KRB5_HEIMDAL_BROKEN_KRB5_H
 
-dnl check the max skew in the krb5 context, and sets squid_cv_max_skew_context
-AC_DEFUN([SQUID_CHECK_MAX_SKEW_IN_KRB5_CONTEXT],[
-  AC_CACHE_CHECK([for max_skew in struct krb5_context],
-                  squid_cv_max_skew_context, [
-    SQUID_STATE_SAVE(squid_krb5_test)
-    CPPFLAGS="-I${srcdir:-.} $CPPFLAGS"
-    AC_COMPILE_IFELSE([
-      AC_LANG_PROGRAM([[
-#include "compat/krb5.h"
-krb5_context kc; kc->max_skew = 1;
-      ]])
-    ],[ squid_cv_max_skew_context=yes ],
-    [ squid_cv_max_skew_context=no ])
-    SQUID_STATE_ROLLBACK(squid_krb5_test)
-  ])
-])
-
 dnl check whether the kerberos context has a memory cache. Sets
 dnl squid_cv_memory_cache if that's the case.
 AC_DEFUN([SQUID_CHECK_KRB5_CONTEXT_MEMORY_CACHE],[
@@ -315,9 +298,6 @@ AC_DEFUN([SQUID_CHECK_KRB5_FUNCS],[
   AC_CHECK_LIB(krb5,krb5_get_init_creds_keytab,
     AC_DEFINE(HAVE_GET_INIT_CREDS_KEYTAB,1,
       [Define to 1 if you have krb5_get_init_creds_keytab]),)
-  AC_CHECK_LIB(krb5,krb5_get_max_time_skew,
-    AC_DEFINE(HAVE_KRB5_GET_MAX_TIME_SKEW,1,
-      [Define to 1 if you have krb5_get_max_time_skew]),)
   AC_CHECK_LIB(krb5,krb5_get_profile,
     AC_DEFINE(HAVE_KRB5_GET_PROFILE,1,
       [Define to 1 if you have krb5_get_profile]),)

src/peer_proxy_negotiate_auth.cc

@@ -307,10 +307,8 @@ int krb5_create_cache(char *kf, char *pn) {
                    error_message(code));
             return (1);
         }
-#elif HAVE_LIBHEIMDAL_KRB5 && HAVE_KRB5_GET_MAX_TIME_SKEW
+#elif HAVE_LIBHEIMDAL_KRB5
         skew = krb5_get_max_time_skew(kparam.context);
-#elif HAVE_LIBHEIMDAL_KRB5 && HAVE_MAX_SKEW_IN_KRB5_CONTEXT
-        skew = kparam.context->max_skew;
 #else
         skew = DEFAULT_SKEW;
 #endif