Description of problem:

When Satellite is integrated for external authentication with IPA using the below guide.

https://access.redhat.com/documentation/en-us/red_hat_satellite/6.2/html-single/server_administration_guide/#sect-Red_Hat_Satellite-Server_Administration_Guide-Configuring_External_Authentication-Integrate_IdM_with_Satellite

The IPA/IDM users are able to login into the Satellite Web UI . But they cannot register the client using the subscription-manager and is not able query the Satellite api. 

Version-Release number of selected component (if applicable):
Satellite 6.2.8

How reproducible:
Every time

Steps to Reproduce:
1. Configure satellite for external authentication with ipa using the below guide

https://access.redhat.com/documentation/en-us/red_hat_satellite/6.2/html-single/server_administration_guide/#sect-Red_Hat_Satellite-Server_Administration_Guide-Configuring_External_Authentication-Integrate_IdM_with_Satellite

2. Try to register one of the system using the IPA user . Or try to call the Satellite api using the curl command.

Actual results:
The IPA users are not able to register the client host to Satellite 6 and also use the api.

Expected results:

The IPA users should be able to register to the Satellite 6 using the subscription manager and call the api too.

Additional info:
[A] We see the below error while registering. 
On the client
====
Registering to: satellite.example.com:443/rhsm
Username: <username>
Password: 
Unauthorized: Invalid credentials for request.
====

In Satellite 6 foreman/production.log file
====
2017-05-26 04:23:07 [app] [I] Started GET "/rhsm/users/<user>/owners" for 192.168.124.100 at 2017-05-26 04:23:07 -0400
2017-05-26 04:23:07 [app] [I] Processing by Katello::Api::Rhsm::CandlepinProxiesController#list_owners as JSON
2017-05-26 04:23:07 [app] [I]   Parameters: {"login"=>"<user>"}
2017-05-26 04:23:07 [katello/cp_proxy] [W] SSO failed
2017-05-26 04:23:07 [app] [I]   Rendered api/v2/errors/unauthorized.json.rabl within api/v2/layouts/error_layout (0.5ms)
2017-05-26 04:23:07 [app] [I] Filter chain halted as :authorize rendered or redirected
2017-05-26 04:23:07 [app] [I] Completed 401 Unauthorized in 7ms (Views: 1.2ms | ActiveRecord: 0.6ms)
====

[B] Invoking api using curl
====
# curl -k -u <username>:'<password>' https://sat.example.com/api/hosts
====

Errors in production log
====
2017-05-26 04:29:09 [app] [I] Started GET "/api/hosts" for 192.168.124.100 at 2017-05-26 04:29:09 -0400
2017-05-26 04:29:09 [app] [I] Processing by Api::V2::HostsController#index as JSON
2017-05-26 04:29:09 [app] [I]   Parameters: {"apiv"=>"v2"}
2017-05-26 04:29:09 [app] [W] SSO failed
2017-05-26 04:29:09 [app] [I]   Rendered api/v2/errors/unauthorized.json.rabl within api/v2/layouts/error_layout (0.4ms)
2017-05-26 04:29:09 [app] [I] Filter chain halted as :authorize rendered or redirected
2017-05-26 04:29:09 [app] [I] Completed 401 Unauthorized in 4ms (Views: 1.0ms | ActiveRecord: 0.5ms)
====