You should understand the prerequisites that are needed to provide WebSphere security propagation.
For WebSphere security propagation the following conditions must be met:
All servers must be the same domain (e.g., mycompany.com).
All servers must be configured to use the same registry (e.g., LDAP server).
All users must be in the same registry.
The browser must have HTTP cookies enabled.
The Web application must be configured for “basic” or “form-based” authentication.
For details, see http://publib.boulder.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=/com.ibm.websphere.nd.doc/info/ae/ae/csec_sso.html.