Integrate support for GSS-API

authentication, implemented by Kevin L. Mitchel <klmitch@mit.edu>.

lib-src/Makefile.in

@@ -205,12 +205,21 @@ MOVE_FLAGS=
 # ifdef HAVE_LIBCOM_ERR
 	COM_ERRLIB = -lcom_err
 # endif
-#endif /* KERBEROS
+# ifdef HAVE_LIBGSSAPI_KRB5
+	GSSAPI_KRB5LIB = -lgssapi_krb5
+# endif
+#endif /* KERBEROS */
+
+#ifdef HAVE_LIBGSSAPI
+	GSSAPILIB = -lgssapi
+#endif
 
-/* If HESIOD is defined, set this to "-lhesiod". */
-HESIODLIB=
+#ifdef HESIOD
+HESIODLIB= -lhesiod
+#endif
 
-MOVE_LIBS=$(KRB4LIB) $(DESLIB) $(KRB5LIB) $(CRYPTOLIB) $(COM_ERRLIB) $(HESIODLIB)
+MOVE_LIBS=$(GSSAPI_KRB5LIB) $(GSSAPILIB) $(KRB4LIB) $(DESLIB) $(KRB5LIB) \
+	$(CRYPTOLIB) $(COM_ERRLIB) $(HESIODLIB)
 
 #ifdef HAVE_LIBMAIL
 LIBMAIL=-lmail

lib-src/pop.h

@@ -36,6 +36,7 @@ struct _popserver
   int buffer_size, buffer_index;
   int in_multi;
   int trash_started;
+  void *extra;
 };
 
 typedef struct _popserver *popserver;
@@ -47,6 +48,30 @@ typedef struct _popserver *popserver;
 #define POP_NO_KERBEROS	(1<<0)
 #define POP_NO_HESIOD	(1<<1)
 #define POP_NO_GETPASS 	(1<<2)
+#define POP_NO_GSSAPI	(1<<3)	/* don't use the GSSAPI */
+#define POP_NO_NOPROT	(1<<4)	/* prohibit no protection; this *only* */
+				/* makes sense if you use GSSAPI */
+#define POP_NO_INTEG	(1<<5)	/* don't use plain integrity */
+#define POP_NO_ENCRYPT	(1<<6)	/* don't use encryption */
+
+/*
+ * GSSAPI documentation
+ *
+ * This version will attempt to perform a GSSAPI handshake first; if this
+ * fails, then it will attempt standard POP authentication.  Note that
+ * library conflicts may prevent the use of this with the Kerberos
+ * kpop hack.
+ *
+ * If you specify POP_NO_NOPROT and this library is unable to provide either
+ * integrity protection or encryption, pop_open() will fail.  The pop_open()
+ * call will attempt the highest level protection available; i.e., if both
+ * server and client support encryption (and you do not provide the
+ * POP_NO_ENCRYPT flag), that will be used; if both server and client support
+ * integrity protection (and you do not provide the POP_NO_INTEG flag), that
+ * will be used.  If neither of these are available, and you have not
+ * specified the POP_NO_NOPROT flag, then this will be a normal, unprotected
+ * connection.
+ */
 
 #ifdef __STDC__
 #define _ARGS(a) a