Provide more detail in postmaster log for password authentication failures.

We tell people to examine the postmaster log if they're unsure why they are getting auth failures, but actually only a few relatively-uncommon failure cases were given their own log detail messages in commit 64e43c5. Expand on that so that every failure case detected within md5_crypt_verify gets a specific log detail message. This should cover pretty much every ordinary password auth failure cause. So far I've not noticed user demand for a similar level of auth detail for the other auth methods, but sooner or later somebody might want to work on them. This is not that patch, though.

Author: tglsfdc

src/backend/libpq/crypt.c

@@ -50,7 +50,11 @@ md5_crypt_verify(const Port *port, const char *role, char *client_pass,
 /* Get role info from pg_authid */
 roleTup = SearchSysCache1(AUTHNAME, PointerGetDatum(role));
 if (!HeapTupleIsValid(roleTup))
+{
+*logdetail = psprintf(_("Role \"%s\" does not exist."),
+ role);
 return STATUS_ERROR;/* no such user */
+}
 
 datum = SysCacheGetAttr(AUTHNAME, roleTup,
 Anum_pg_authid_rolpassword, &isnull);
@@ -71,13 +75,20 @@ md5_crypt_verify(const Port *port, const char *role, char *client_pass,
 ReleaseSysCache(roleTup);
 
 if (*shadow_pass == '\0')
+{
+*logdetail = psprintf(_("User \"%s\" has an empty password."),
+ role);
 return STATUS_ERROR;/* empty password */
+}
 
 CHECK_FOR_INTERRUPTS();
 
 /*
  * Compare with the encrypted or plain password depending on the
- * authentication method being used for this connection.
+ * authentication method being used for this connection. (We do not
+ * bother setting logdetail for pg_md5_encrypt failure: the only possible
+ * error is out-of-memory, which is unlikely, and if it did happen adding
+ * a psprintf call would only make things worse.)
  */
 switch (port->hba->auth_method)
 {
@@ -154,6 +165,9 @@ md5_crypt_verify(const Port *port, const char *role, char *client_pass,
 else
 retval = STATUS_OK;
 }
+else
+*logdetail = psprintf(_("Password does not match for user \"%s\"."),
+ role);
 
 if (port->hba->auth_method == uaMD5)
 pfree(crypt_pwd);