zhaorui

Hope this pr could solve issues about ldap like https://github.com/pgbouncer/pgbouncer/issues/469. The implementation is a combination of postgres ldap authentication and PAM thread model.

> The LDAP is used in the same way as Postgres. The configuration is shown in the commit comments as an example. Since this PR refers a lot to PAM...

> I have rebased the master and all the testings have passed. There are ldap testings in gpdb, I will try to add it to test cases later. But the...

I have added LDAP test cases in some of ubuntu platforms. If configured without `--with-ldap` or no ldapadd command installed, the ldap test will be skipped.

This previous PR https://github.com/greenplum-db/gpdb/pull/3608/files has added a lot of FRONTEND macro in codes. I have checked most of them that I think we should remove these lines: https://github.com/greenplum-db/gpdb/blob/bbad4c972334b6d868da7f260a52e66a51cebb12/src/interfaces/libpq/libpq-fe.h#L226-L229. But there...

Thanks for your comments. I have fix most of the code styles that you have mentioned. But some of them can not be easily fixed so I will give each...

> I'm not referring to connect to Postgres on a Windows server. PgBouncer won't compile on Windows if you don't add some Windows-specific code paths. Refer to `winldap.h`. > I...

> Indeed. But if you are using a centralized authentication mechanism, you don't want it to be bypassed by another mechanism that you can easily introduce adding a new entry...

> Ooops. I didn't think carefully while suggesting ldap.h. What about `ldapauth.[ch]`? There is no such file name with `bouncer` prefix. OK, `ldapauth.[ch]` is better I think. > > What...

> Wait. The `ldapbinddn` and `ldapbindpasswd` parameters are fixed for PostgreSQL as well. You normally use **only one** credential to bind and perform a search using `ldapsearchattribute` (or `uid` if...