How do I authenticate with Spnego/Kerberos and Apache's HttpClient?

Question

How do I correctly setup a connection with HttpClient that uses the logged in user's ActiveDirectory credentials to authenticate against a website and requires Kerberos/Spnego authentication?

Answer 1

Here's an example:

public class HttpSpnegoConnection {
        
    /**
     * Uses HttpClient 4.3.4 and CommonsIO 2.4
     */
    public static void main(String[] args) throws ClientProtocolException, IOException {
        
        
        String domain = "yourdomain.com";
        String kdc =  "thekdc.yourdomain.ch";
        // careful with aliases, 'somewebsite' has to be in the kerberos database
        String url = "http://somewebsite:8080/myresource/";
        // if the port does not match the kerberos database entry, skip it during the lookup
        boolean skipPortAtKerberosDatabaseLookup = true;

        // Depending on your AD configuration, this file is not needed
        File krb5Config = createKrb5Configuration(domain,kdc);
        
        System.out.println("Created config '"+krb5Config.getAbsolutePath()+"':");
        System.out.println(IOUtils.toString(new FileReader(krb5Config)));
        
        System.setProperty("java.security.krb5.conf", krb5Config.toURI().toString());
        System.setProperty("sun.security.krb5.debug", "true");
        System.setProperty("javax.security.auth.useSubjectCredsOnly","false");
        
        
        Lookup<AuthSchemeProvider> authSchemeRegistry = RegistryBuilder.<AuthSchemeProvider>create()
            .register(AuthSchemes.SPNEGO, new SPNegoSchemeFactory(skipPortAtKerberosDatabaseLookup))
            .build();
        
        CloseableHttpClient client = HttpClients.custom().setDefaultAuthSchemeRegistry(authSchemeRegistry).build();
        HttpClientContext context = HttpClientContext.create();
        BasicCredentialsProvider credentialsProvider = new BasicCredentialsProvider();

        // This may seem odd, but specifying 'null' as principal tells java to use the logged in user's credentials
        Credentials useJaasCreds = new Credentials() {

            public String getPassword() {
                return null;
            }

            public Principal getUserPrincipal() {
                return null;
            }

        };
        credentialsProvider.setCredentials( new AuthScope(null, -1, null), useJaasCreds );
        context.setCredentialsProvider(credentialsProvider);
        
        HttpGet httpget = new HttpGet(url);
        CloseableHttpResponse response = client.execute(httpget,context);
        String responseString = IOUtils.toString(response.getEntity().getContent());
        
        System.out.println("HTTP Response:");
        System.out.println(responseString);
    }
    
    /** 
        Creates a temporary krb5.conf
        [libdefaults]
            default_realm = <domain>
            
        [realms]
            snb.ch = {
                kdc = <kdc>
                admin_server = <kdc>
            }
     */
    private static File createKrb5Configuration(String domain, String kdc) throws IOException {
        File tempFile = File.createTempFile("krb5", "kdc");
        ArrayList<String> lines = new ArrayList<>();
        lines.add("[libdefaults]");
        lines.add("\tdefault_realm = "+domain);
        lines.add("[realms]");
        lines.add("\t"+domain+" = {");
        lines.add("\t\tkdc = "+kdc);
        lines.add("\t\tadmin_server = "+kdc);
        lines.add("\t}");
        FileWriter writer = new FileWriter(tempFile);
        IOUtils.writeLines(lines, System.lineSeparator(), writer);
        IOUtils.closeQuietly(writer);
        return tempFile;
    }
    
}

Depending on your AD configuration, creating and specifying the krb5.conf may be skipped.