UserService API/SPI with Impersonation

This module (incode-module-userimpersonate-dom) overrides the default implementation of Apache Isis' UserService API. Intended for prototyping and demos only, it allows the logged-in user to be switched dynamically, ie to impersonate some other user.


The UserService API is defined as:

public interface UserService {
    UserMemento getUser();

where UserMemento contains both the current user name and their set of roles.

The Apache Isis framework provide a default implementation of this service. What this module does is to provide a different implementation of the service with a higher priority which is therefore used instead.

This implementation - UserServiceWithImpersonation - extends the API as follows:

public class UserServiceWithImpersonation implements UserService {

    public UserMemento getUser() { ... }                                (1)

    public void setUser(String userName) { ... }                        (2)
    public void setUser(String userName, String... roles) { ... }
    public void setUser(String userName, List<String> roles) { ... }

    public void reset() { ... }                                         (3)

    public boolean isImpersonating() { ... }                            (4)

    public boolean isAvailable() { ... }                                (5)
1 the API of UserService, this returns the current user. If a user is being impersonated (per setUser(…​)) then that will be returned.
2 Impersonate a different user, optionally specifying a different set of roles. If roles are not specified then the roles of the original user are preserved.
3 Removes the impersonation, returning back to the original user.
4 Check to see if a user is being impersonated (that is, that setUser(…​) was called and reset() has not been called subsequently).
5 Checks that the service is available. If it is not, then setUser(…​) has no effect.

The service is only available when running within a webapp. This is because it relies upon the HttpSession (as obtained from Servlet API module) to store the impersonating user identity.

Note that impersonations do not nest.

That is, the user logs in as user1, then impersonates to user2, then impersonates again to user3, then resetting will go back to the original user1.

Menus and Contributions

The ImpersonationMenu domain service provides a couple of actions which are surfaced in the UI on the tertiary menu bar:

public class ImpersonateMenu {

    public void impersonate(
            ApplicationUser applicationUser,
            List<ApplicationRole> applicationRoleList) { ... }

    public void stopImpersonating() { ... }

This uses the Security module to constrain the list of valid users/roles.

There are also two mixins:

  • the Object_impersonateUser mixin allows impersonation to be invoked from any domain object.

  • the Object_stopImpersonating mixin similarly resets impersonation.

The actions of the menu and the mixins are restricted to prototyping only. They also emit domain events so can be vetoed if required.

Behind the scenes these classes delegate to the module’s ImpersonationService, mostly an implementation detail:

public class ImpersonationService {

    public void impersonate(
            ApplicationUser applicationUser,
            List<ApplicationRole> applicationRoleList) { ... }
    public boolean hideImpersonate() { ... }

    public void stopImpersonating() { ... }
    public boolean hideStopImpersonating() { ... }

How to configure/use


Update your classpath by adding this dependency in your dom project’s pom.xml:


Check for later releases by searching Maven Central Repo.


In the AppManifest, update its getDependencies() method, eg:

public Set<Module> getDependencies() {
    return Sets.newHashSet(
            new org.incode.module.userimpersonate.UserImpersonateModule(),

Known issues

None known at this time.


Maven can report modules dependencies using:

mvn dependency:list -o -pl modules/spi/userimpersonate/impl -D excludeTransitive=true

which, excluding Apache Isis itself, depends only on the ServletAPI library module and the Security SPI module