Description of problem:

Currently in SSSD when you want to use only an id_provider and don't want to
use an auth_provider for a certain backend (for example NIS) you will need to
create an empty proxy_pam_target file. This is needed because if you leave the
auth_provider empty (because you aren ot using one) SSSD will assume the same
value applies as is used for id_provider and you are required to enter a value
for proxy_pam_target for SSSD to start up correctly.

Version-Release number of selected component (if applicable):

sssd-1.5.1-66.el6_2.3.x86_64

How reproducible:

Configure SSSD to use a backend that only requires an id_provider and leave the
auth_provider empty.

Steps to Reproduce:
1. Configure SSSD as follows:

[sssd]
config_file_version = 2
services = nss, pam
domains = lab

[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3
entry_cache_timeout = 300
entry_cache_nowait_percentage = 75
pwfield = x

[pam]

[domain/lab]
id_provider = proxy
proxy_lib_name = nis

Note: there is no proxy_pam_target directive

2. Start up SSSD, you will see the following error:

(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [load_backend_module] (7): Loading
backend [proxy] with path [/usr/lib64/sssd/libsss_proxy.so].
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [load_backend_module] (5): no module
name found in confdb, using [proxy].
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [load_backend_module] (7): Backend
[proxy] already loaded.
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [sssm_proxy_auth_init] (1): Missing
option proxy_pam_target.
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [load_backend_module] (0): Error
(22) in module (proxy) initialization (sssm_proxy_auth_init)!
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [be_process_init] (0): fatal error
initializing data providers
(Tue May 15 16:06:14 2012) [sssd[be[lab]]] [main] (0): Could not initialize
backend [22]

3. SSSD now does not function.

4. Now add proxy_pam_target to the lab domain:
[domain/lab]
id_provider = proxy
proxy_lib_name = nis
proxy_pam_target = sss_lab

5. Create an empty file /etc/pam.d/sss_lab

6. Start SSSD, you will see it start properly.

Actual results:

SSSD starts but "fake" configuration directives are needed to get it to start.

Expected results:

You can configure SSSD to not use an auth_provider so that it is clear from the
configuration file no auth_provider is used.

Additional info: