How do you authenticate against an Active Directory server using Spring Security?

Question

I\'m writing a Spring web application that requires users to login. My company has an Active Directory server that I\'d like to make use of for this purpose. However, I\'m

Answer 1

I had the same banging-my-head-against-the-wall experience you did, and ended up writing a custom authentication provider that does an LDAP query against the Active Directory server.

So my security-related beans are:

Then the LdapAuthenticationProvider class:

/**
 * Custom Spring Security authentication provider which tries to bind to an LDAP server with
 * the passed-in credentials; of note, when used with the custom {@link LdapAuthenticatorImpl},
 * does not require an LDAP username and password for initial binding.
 * 
 * @author Jason
 */
public class LdapAuthenticationProvider implements AuthenticationProvider {

    private LdapAuthenticator authenticator;

    public Authentication authenticate(Authentication auth) throws AuthenticationException {

        // Authenticate, using the passed-in credentials.
        DirContextOperations authAdapter = authenticator.authenticate(auth);

        // Creating an LdapAuthenticationToken (rather than using the existing Authentication
        // object) allows us to add the already-created LDAP context for our app to use later.
        LdapAuthenticationToken ldapAuth = new LdapAuthenticationToken(auth, "ROLE_USER");
        InitialLdapContext ldapContext = (InitialLdapContext) authAdapter
                .getObjectAttribute("ldapContext");
        if (ldapContext != null) {
            ldapAuth.setContext(ldapContext);
        }

        return ldapAuth;
    }

    public boolean supports(Class clazz) {
        return (UsernamePasswordAuthenticationToken.class.isAssignableFrom(clazz));
    }

    public LdapAuthenticator getAuthenticator() {
        return authenticator;
    }

    public void setAuthenticator(LdapAuthenticator authenticator) {
        this.authenticator = authenticator;
    }

}

Then the LdapAuthenticatorImpl class:

/**
 * Custom Spring Security LDAP authenticator which tries to bind to an LDAP server using the
 * passed-in credentials; does not require "master" credentials for an
 * initial bind prior to searching for the passed-in username.
 * 
 * @author Jason
 */
public class LdapAuthenticatorImpl implements LdapAuthenticator {

    private DefaultSpringSecurityContextSource contextFactory;
    private String principalPrefix = "";

    public DirContextOperations authenticate(Authentication authentication) {

        // Grab the username and password out of the authentication object.
        String principal = principalPrefix + authentication.getName();
        String password = "";
        if (authentication.getCredentials() != null) {
            password = authentication.getCredentials().toString();
        }

        // If we have a valid username and password, try to authenticate.
        if (!("".equals(principal.trim())) && !("".equals(password.trim()))) {
            InitialLdapContext ldapContext = (InitialLdapContext) contextFactory
                    .getReadWriteContext(principal, password);

            // We need to pass the context back out, so that the auth provider can add it to the
            // Authentication object.
            DirContextOperations authAdapter = new DirContextAdapter();
            authAdapter.addAttributeValue("ldapContext", ldapContext);

            return authAdapter;
        } else {
            throw new BadCredentialsException("Blank username and/or password!");
        }
    }

    /**
     * Since the InitialLdapContext that's stored as a property of an LdapAuthenticationToken is
     * transient (because it isn't Serializable), we need some way to recreate the
     * InitialLdapContext if it's null (e.g., if the LdapAuthenticationToken has been serialized
     * and deserialized). This is that mechanism.
     * 
     * @param authenticator
     *          the LdapAuthenticator instance from your application's context
     * @param auth
     *          the LdapAuthenticationToken in which to recreate the InitialLdapContext
     * @return
     */
    static public InitialLdapContext recreateLdapContext(LdapAuthenticator authenticator,
            LdapAuthenticationToken auth) {
        DirContextOperations authAdapter = authenticator.authenticate(auth);
        InitialLdapContext context = (InitialLdapContext) authAdapter
                .getObjectAttribute("ldapContext");
        auth.setContext(context);
        return context;
    }

    public DefaultSpringSecurityContextSource getContextFactory() {
        return contextFactory;
    }

    /**
     * Set the context factory to use for generating a new LDAP context.
     * 
     * @param contextFactory
     */
    public void setContextFactory(DefaultSpringSecurityContextSource contextFactory) {
        this.contextFactory = contextFactory;
    }

    public String getPrincipalPrefix() {
        return principalPrefix;
    }

    /**
     * Set the string to be prepended to all principal names prior to attempting authentication
     * against the LDAP server.  (For example, if the Active Directory wants the domain-name-plus
     * backslash prepended, use this.)
     * 
     * @param principalPrefix
     */
    public void setPrincipalPrefix(String principalPrefix) {
        if (principalPrefix != null) {
            this.principalPrefix = principalPrefix;
        } else {
            this.principalPrefix = "";
        }
    }

}

And finally, the LdapAuthenticationToken class:

/**
 * 

 * Authentication token to use when an app needs further access to the LDAP context used to
 * authenticate the user.
 * 
 * 
 * 

 * When this is the Authentication object stored in the Spring Security context, an application
 * can retrieve the current LDAP context thusly:
 * 
 * 
 * 
 * LdapAuthenticationToken ldapAuth = (LdapAuthenticationToken) SecurityContextHolder
 *      .getContext().getAuthentication();
 * InitialLdapContext ldapContext = ldapAuth.getContext();
 * 
 * 
 * @author Jason
 * 
 */
public class LdapAuthenticationToken extends AbstractAuthenticationToken {

    private static final long serialVersionUID = -5040340622950665401L;

    private Authentication auth;
    transient private InitialLdapContext context;
    private List authorities = new ArrayList();

    /**
     * Construct a new LdapAuthenticationToken, using an existing Authentication object and
     * granting all users a default authority.
     * 
     * @param auth
     * @param defaultAuthority
     */
    public LdapAuthenticationToken(Authentication auth, GrantedAuthority defaultAuthority) {
        this.auth = auth;
        if (auth.getAuthorities() != null) {
            this.authorities.addAll(Arrays.asList(auth.getAuthorities()));
        }
        if (defaultAuthority != null) {
            this.authorities.add(defaultAuthority);
        }
        super.setAuthenticated(true);
    }

    /**
     * Construct a new LdapAuthenticationToken, using an existing Authentication object and
     * granting all users a default authority.
     * 
     * @param auth
     * @param defaultAuthority
     */
    public LdapAuthenticationToken(Authentication auth, String defaultAuthority) {
        this(auth, new GrantedAuthorityImpl(defaultAuthority));
    }

    public GrantedAuthority[] getAuthorities() {
        GrantedAuthority[] authoritiesArray = this.authorities.toArray(new GrantedAuthority[0]);
        return authoritiesArray;
    }

    public void addAuthority(GrantedAuthority authority) {
        this.authorities.add(authority);
    }

    public Object getCredentials() {
        return auth.getCredentials();
    }

    public Object getPrincipal() {
        return auth.getPrincipal();
    }

    /**
     * Retrieve the LDAP context attached to this user's authentication object.
     * 
     * @return the LDAP context
     */
    public InitialLdapContext getContext() {
        return context;
    }

    /**
     * Attach an LDAP context to this user's authentication object.
     * 
     * @param context
     *          the LDAP context
     */
    public void setContext(InitialLdapContext context) {
        this.context = context;
    }

}

You'll notice that there are a few bits in there that you might not need.

For example, my app needed to retain the successfully-logged-in LDAP context for further use by the user once logged in -- the app's purpose is to let users log in via their AD credentials and then perform further AD-related functions. So because of that, I have a custom authentication token, LdapAuthenticationToken, that I pass around (rather than Spring's default Authentication token) which allows me to attach the LDAP context. In LdapAuthenticationProvider.authenticate(), I create that token and pass it back out; in LdapAuthenticatorImpl.authenticate(), I attach the logged-in context to the return object so that it can be added to the user's Spring authentication object.

Also, in LdapAuthenticationProvider.authenticate(), I assign all logged-in users the ROLE_USER role -- that's what lets me then test for that role in my intercept-url elements. You'll want to make this match whatever role you want to test for, or even assign roles based on Active Directory groups or whatever.

Finally, and a corollary to that, the way I implemented LdapAuthenticationProvider.authenticate() gives all users with valid AD accounts the same ROLE_USER role. Obviously, in that method, you can perform further tests on the user (i.e., is the user in a specific AD group?) and assign roles that way, or even test for some condition before even granting the user access at all.