Configuring Servlet-Container Authentication

Servlet containers have different mechanisms to create the user Principal object and run security checks when authentication is required for secured endpoints.

As a reference, we provide configuration examples of custom session-based authentication with two popular containers.

Session-Based Authentication

Configuring a Custom Servlet Filter

For customized authentication, you need to implement a custom HttpServletRequest to wrap the default authentication using a WebFilter.

The following example contains a customized Principal object. It is assumed that this principal is set as a Session attribute at some point by the application.

public class CustomPrincipal implements Principal {
    private final String name;
    private final List<String> roles;

    public CustomPrincipal(String name, String ...roles) {
        this.name = name;
        this.roles = Arrays.asList(roles);
    }

    public String getName() {
        return name;
    }

    public boolean isUserInRole(String role) {
        return roles.contains(role);
    }
}

public class CustomHttpServletRequest extends HttpServletRequestWrapper {
    public CustomHttpServletRequest(HttpServletRequest request) {
        super(request);
    }

    @Override
    public Principal getUserPrincipal() {
        Principal myUser = (Principal) getSession().getAttribute("User");
        return myUser != null ? myUser : super.getUserPrincipal();
    }

    @Override
    public boolean isUserInRole(String role) {
        return getUserPrincipal() instanceof CustomPrincipal
                && ((CustomPrincipal) getUserPrincipal()).isUserInRole(role)
                || super.isUserInRole(role);
    }
}

@WebFilter("/connect")
public class CustomWebFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        chain.doFilter(new CustomHttpServletRequest((HttpServletRequest) request), response);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException { }

    @Override
    public void destroy() { }
}

Configuring a Client Log-in Form

Create a form to ask the user for a username/password pair and send it to the server side. The following snippet shows how to code a log-in web component.

import { html, LitElement } from 'lit';
import { customElement, query } from 'lit/decorators.js';

@customElement("my-login")
export class MyLogin extends LitElement {
  @query('#username')
  private username: any;
  @query('#password')
  private password: any;

  render() {
    return html`
      <input id="username" name="username"></input>
      <input id="password" name="password" type="password"></input>
      <button @click="${this.login}">login</button>
    `;
  }

  private login() {
    fetch('/connect/login', {
      method: 'POST',
      body: `username=${this.username.value}&password=${this.password.value}`
    })
    .then(() => console.log("User Logged-in"));
  }
}

Next, change the above filter to handle the request and set the appropriate principal object in the session.

@WebFilter("/connect")
public class CustomWebFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        // Check username/password and set the `User` attribute in session
        if ("foo".equals(request.getParameter("username")) &&
            "abc123".equals(request.getParameter("password"))) {
            ((HttpServletRequest) request).getSession()
                .setAttribute("User", new CustomPrincipal("foo"));
        }

        // wrap original request with our custom implementation
        chain.doFilter(new CustomHttpServletRequest((HttpServletRequest) request), response);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException { }
    @Override
    public void destroy() { }
}