This guide walks through the process of creating an user impersonation from super / admin users with spring security.

Overview

It’s a common use-case for secured applications that the admin / super users to be able to login as any other user. It can be helpful for use cases such as customer support analysis where the analyst can access the system as the real user.

A possible solution for that would be asking for the customer’s password or get it from the database. This solution is nothing else than a security breach. If the password storage is implemented correctly it should be impossible to recover the customer’s password.

To solve that problem it would be possible for super / admin users to impersonate any other specific user without the need for the target user’s password. With a proper user impersonation implementation in place, the system knows who has really logged in and it can be used to track the super user’s action if there’s an audit log in place.

It’s a lot to implement from scratch, luckily this feature is present in spring security.

Meet SwitchUserFilter

SwitchUserFilter is a Filter responsible for user context switching.

From the javadoc:

This filter is similar to Unix ‘su’ however for Spring Security-managed web applications. A common use-case for this feature is the ability to allow higher-authority users (e.g. ROLE_ADMIN) to switch to a regular user (e.g. ROLE_USER).

This filter requires the following properties:

@Bean
public SwitchUserFilter switchUserFilter() {
    SwitchUserFilter filter = new SwitchUserFilter();
    filter.setUserDetailsService(userDetailsService());
    filter.setSwitchUserUrl("/impersonate");
    filter.setSwitchFailureUrl("/switchUser");
    filter.setTargetUrl("/hello");
    return filter;
}

SwitchUserFilter Form

Now we need to define an HTML form that’s going to be used to switch the users.

<form method="GET" th:action="@{/impersonate}" class="form">
    <label for="usernameField">User name:</label>
    <input type="text" name="username" id="usernameField" />
    <input type="submit" value="Switch User" />
</form>

Here are some remarks

• The value defined in the action needs the same value defined by the SwitchUserFilter#switchUserUrl property.
• It can be a GET request.
• The request is handled by the SwitchUserFilter.

Securing the form

It’s necessary to make sure that only ADMIN users will be able to reach the impersonate form, otherwise, any user will be able to switch to another user’s account without the need of the password.

Add the following piece of code to the security configuration.

http.authorizeRequests()
        .antMatchers("/switchUser").access("hasRole('ADMIN')");

Now, if any other user tries to access the /switchUser URL, they will get an HTTP 403 Forbidden response.

Who is really logged in?

This mechanism totally switches the Authentication object in the SecurityContext, it means, if you look at the current user’s permissions or roles, you’ll get the impersonated user’s values, not the ADMIN user.

Spring Security by default adds a new role ROLE_PREVIOUS_ADMINISTRATOR to the impersonated user. So to make it easier to go back to the ADMIN user, we need to add this role to the security configuration.

http.authorizeRequests()
        .antMatchers("/switchUser").access("hasAnyRole('ADMIN', 'ROLE_PREVIOUS_ADMINISTRATOR')");

Summary

Congratulations! You just created a user impersonation filter using spring security.

Footnote

• The code used for this tutorial can be found on github