Getting hold of workspace for user session

We're in the process of separating our entire workspace into multiple workspaces. As part of the code restructuring we're stuck at one place. At the moment we get hold of the user session using 

request.getResourceResolver().adaptTo(Session.class);

What this does is that it returns back is the session for the default workspace (crx.default). Is there a way we can get hold of  a specified workspace? I can see that the Repository class has the 

repository.login(Crendentials, WorkspaceName)

However we weren't able to find out a way to get the Credentials from the Session. The authentication right now is integrated with LDAP.

Is there any workaround for this?