Can't access the SOA webservicess WSIL on an OBIEE11g instance using SSO with WNA

[S.]

PROBLEM DEFINITION

We can't access the SOA WebServicess WSIL on an OBIEE (v.11.1.1.7.131017) instance using SSO with WNA. The OBIEE instance is using SSO + WNA using kerberos. The http://server:port/analytics is PROTECTED by the SSO challenge. 

DETAILED STEPS

To enable the SOA web services, we did the following configuration (following the instructions in: http://docs.oracle.com/cd/E28280_01/bi.1111/e16364/soa_overview.htm#CEGHCJCJ) 

1 - Create a credential key in EM called wsil.browsing associated to a valid username/password 

2 - Restart the managed bi_server1 and the presentation services. 

3 - Try to access the http://server:port/biservices/inspection?wsil 

4 - We get Error 500 - Internal. 

After checking the nqserver.log I can see the following error: 

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oracle.bi.ws.activeobjects.bipresentation.BiPresentationServerCommsException: bi services:bi presentation services(SessionService) Could not access the session service 2 counts of InaccessibleWSDLException. 

at oracle.bi.ws.activeobjects.security.OBIPSWebServiceFactory.getSessionService(OBIPSWebServiceFactory.java:87) 

at oracle.bi.ws.activeobjects.security.Server.loginWebService(Server.java:118) 

.... 

Caused By: com.sun.xml.ws.wsdl.parser.InaccessibleWSDLException: 2 counts of InaccessibleWSDLException. 

java.io.FileNotFoundException: Response: '401: Unauthorized' for url: 'http://server:9704/analytics/saw.dll/wsdl/v8' 

java.io.FileNotFoundException: Response: '401: Unauthorized' for url: 'http://server:9704/analytics/saw.dll/wsdl/v8?wsdl' 

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We tested the same approach on an installation without SSO and the process was successful and we could access the inspection?wisl. 

QUESTION

Do you know what configuration steps do we need to take to configure SOA webservices on a SSO+WNA protected OBIEE installation?