Description of problem:

For a long time, we've recommended adding mail to ldap_user_extra_attrs when it
should be made available via ifp, for example at

   http://www.freeipa.org/page/Web_App_Authentication/Example_setup

Now that change causes SSSD to fail to start.

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

sssd-1.14.0-14.el7.x86_64

How reproducible:

Deterministic.

Steps to Reproduce:
1. Put line ldap_user_extra_attrs = mail, firstname:givenname, lastname:sn to
[domain/*] section of sssd.conf on IPA-enrolled machine.
2. Run systemctl restart sssd

Actual results:

Job for sssd.service failed because the control process exited with error code.
See "systemctl status sssd.service" and "journalctl -xe" for details.

Aug 01 04:02:09 client.example.test sssd[be[example.test]][5624]: Starting up
Aug 01 04:02:10 client.example.test sssd[be[example.test]][5625]: Starting up
Aug 01 04:02:12 client.example.test sssd[be[example.test]][5626]: Starting up
Aug 01 04:02:15 client.example.test sssd[pam][5637]: Starting up
Aug 01 04:02:16 client.example.test sssd[be[example.test]][5639]: Starting up
Aug 01 04:02:16 client.example.test sssd[5623]: Exiting the SSSD. Could not
restart critical service [example.test].
Aug 01 04:02:16 client.example.test systemd[1]: sssd.service: control process
exited, code=exited status=1
Aug 01 04:02:16 client.example.test systemd[1]: Failed to start System Security
Services Daemon.
Aug 01 04:02:16 client.example.test systemd[1]: Unit sssd.service entered
failed state.
Aug 01 04:02:16 client.example.test systemd[1]: sssd.service failed.

/var/log/sssd/sssd_example.test.log contains

(Mon Aug  1 03:58:40 2016) [sssd[be[example.test]]] [sdap_extend_map] (0x0010):
Attribute mail (mail in LDAP) is already used by SSSD, please choose a
different cache name
(Mon Aug  1 03:58:40 2016) [sssd[be[example.test]]] [dp_module_run_constructor]
(0x0010): Module [ipa] constructor failed [1432158247]: Extra attribute is a
duplicate
(Mon Aug  1 03:58:40 2016) [sssd[be[example.test]]] [dp_target_init] (0x0010):
Unable to load module ipa
(Mon Aug  1 03:58:40 2016) [sssd[be[example.test]]] [be_process_init] (0x0010):
Unable to setup data provider [1432158209]: Internal Error
(Mon Aug  1 03:58:40 2016) [sssd[be[example.test]]] [main] (0x0010): Could not
initialize backend [1432158209]

Expected results:

No error, SSSD starts just fine.

Additional info: