I believe the recommended way to do this in Spring Security is with the Domain Access Control lists, see GrantedAuthoritySid @
http://static.springsource.org/spring-security/site/docs/3.1.x/reference/domain-acls.html
However, impersonating another user is more than just having a "delegate identity", you should also consider the implications on logging:
- Do you want your logging to appear as Original User or Impersonated User (or both?)
- Do you want the "impersonation" to show only what the impersonated user sees, or the superset of permissions of the Original User and Impersonated User?
Yet another possibility is to create a "log in as" feature, which essentially changes the principal identity of the current session - or starts a new session with the impersonated identity.
In all of the above, you may inadvertantly open up a security issue - so I think this is why impersonate-style features are not that common place. Rather, designs trend towards Role Based Access Control (RBAC) or Attribute Based Access Control (ABAC). Using RBAC / ABAC, you could create a delegate style feature where you create delegate attributes/roles - and in the special cases where you need to show the source/target of the delegation (e.g. for audit logs), you handle those as corner cases.