Tag: Kerberos

PPM Via Windows Authenticated Proxy

The office proxy used to use BASIC authentication. Which was terrible: transmission was done over clear text. Some years ago, they implemented a new proxy server that was capable of using Kerberos tickets for authentication (actually the old one could have done it too – I’ve set up the Kerberos realm on another implementation of the same product, but it wasn’t a straight forward clickity-click and you’re done). Awesome move, but it did break everything that used the HTTP_PROXY environment variable with creds included (yeah, I have a no-rights account with proxy access and put that in clear text all over the place). I just stopped using wget and curl to download files. I’d pull them to my Windows box, then scp them to the right place. But every once in a while I need a new perl module that’s available from ActiveState’s PPM. I’d have to fetch the tgz file and install it manually.

Until today — I was configuring a new Fiddler installation. Brilliant program – it’s just a web proxy that you can use for debugging purposes, but it can insert itself into HTTPS communications and provide clear text rendering of encrypted sessions too. It also proxies proxy credentials! There’s a config to allow remote hosts to connect – it’s normally bound to, but it can bind to as well. If you have your web browser open & visit a site through the proxy server (i.e. you make sure the browser is authenticating fine) … set your HTTP_PROXY to (or whatever means the specific program uses to configure a proxy). Voila, PPM hits Fiddler. Fiddler relays the request out to the proxy using the Kerberos token on your desktop. Package installs. Lot of overhead just to avoid unzipping a file … but if you are installing a package with a dozen dependencies … well, it’s a lot quicker than failing your install a dozen times and getting the next prereq!

Kerberos Authentication on Tomcat

I finally got around to testing out TomCat 8 and setting up Kerberos authentication for a “single sign-on” experience (i.e. it re-uses the domain logon Kerberos token to authenticate users). This was all done in a docker image, so the config files can be stashed and re-used by anyone with Docker.

First you need an account – on the account properties page, the DES encryption needs to be unchecked and the two AES ones need to be checked. The account then needs to have a service principal name mapped to it. That name will be based on the URL used to access the site. In my case, my site is http://lisa.rushworth.us:8080 (SPNs don’t mind http/https or port numbers) so my SPN is HTTP/lisa.rushworth.us … to set the SPN, run

setspn -A HTTP/lisa.rushworth.us sAMAccountNameOfMyNewlyCreatedAccount

Then generate the keytab:

ktpass /out .\lisa.rushworth.us.keytab /mapuser sAMAccountNameOfMyNewlyCreatedAccount@RUSHWORTH.US /princ HTTP/lisa.rushworth.us@RUSHWORTH.US /pass P@ssw0rdG03sH3r3

** Note about keytabs – there is a KVNO (key version number) associated with a keytab file. When security-related attributes on the account are changed, the KVNO is incremented. Aaaand you need a new keytab. This means you need to be able to get a new keytab if you plan on changing the account password, but it also means that tweaking account settings can render your keytab useless. Get the account all sorted (check off password never expires if that’s what you want, check off user cannot change password, etc) and then generate the keytab.

While you’re working on getting the SPN and keytab stuff sorted, get docker installed and running on your box. I use Docker CE (free) on my Windows laptop, and I’ve had to disable the firewall to allow access from external clients. I would expect a rule (esp one allowing anything to make an inbound connection to 8080/tcp!) would sort it, but I’ve always had the port show as filtered until the firewall is turned off. YMMV.

I create a folder for files mapped into docker containers (i.e. c:\docker) and sub-folders for each specific container. All of the files from TomcatKerberosConfigFiles are unzipped into that folder. The test website is named lisa.rushworth.us and is either set up in DNS or added to c:\windows\system32\drivers\etc\hosts on the client(s) that will access the site. And, of course, there’s a client machine somewhere logged onto the domain. You are going to need to tweak my config files for your domain.

In jaas.conf — I have debug on. Good for testing and playing around, bad for production use. Also you’ll need your SPN and keytab file name


In krb5.conf — the encryption is about the only thing you can keep. Use your hostnames and domain name (REALM). If you have multiple domain controllers, you can have more than one “kdc = ” line in the realms.

default_realm = RUSHWORTH.US
default_keytab_name = /usr/local/tomcat/conf/lisa.rushworth.us.keytab
default_tkt_enctypes = aes128-cts rc4-hmac des3-cbc-sha1 des-cbc-md5 des-cbc-crc
default_tgs_enctypes = aes128-cts rc4-hmac des3-cbc-sha1 des-cbc-md5 des-cbc-crc
permitted_enctypes = aes128-cts rc4-hmac des3-cbc-sha1 des-cbc-md5 des-cbc-crc

kdc = exchange01.rushworth.us:88
master_kdc = exchange01.rushworth.us:88
admin_server = exchange01.rushworth.us:88

rushworth.us= RUSHWORTH.US
.rushworth.us= RUSHWORTH.US

In web.xml – Roles may need to be sorted around (I’m not much of a TomCat person, LMGTFY if you want to do something with roles). Either way, the realm needs to be changed to yours


Once Docker is running and the files are updated with your domain info, install the tomcat:8.0 image from the default repository. Start the container mapping all of the custom config files where they go:

docker run -detach --publish 8080:8080 --name tomcat8 --restart always -v /c/docker/tomcat8/tomcat-users.xml:/usr/local/tomcat/conf/tomcat-users.xml:ro -v /c/docker/tomcat8/lisa.rushworth.us.keytab:/usr/local/tomcat/conf/lisa.rushworth.us.keytab:ro -v /c/docker/tomcat8/krb5.conf:/usr/local/tomcat/conf/krb5.conf:ro -v /c/docker/tomcat8/jaas.conf:/usr/local/tomcat/conf/jaas.conf:ro -v /c/docker/tomcat8/web.xml:/usr/local/tomcat/webapps/examples/WEB-INF/web.xml:ro -v /c/docker/tomcat8/context.xml:/usr/local/tomcat/webapps/examples/WEB-INF/context.xml:ro -v /c/docker/tomcat8/logging.properties:/usr/local/tomcat/conf/logging.properties:ro -v /c/docker/tomcat8/spnego-r9.jar:/usr/local/tomcat/lib/spnego-r9.jar:ro -v /c/docker/tomcat8/login.conf:/usr/local/tomcat/conf/login.conf:ro -v /c/docker/tomcat8/testAuth.jsp:/usr/local/tomcat/webapps/examples/testAuth.jsp:ro tomcat:8.0

A couple of useful things about Docker — the container ID is useful

C:\docker\tomcat8>docker ps
4e06b32e1ca8 tomcat:8.0 "catalina.sh run" 12 minutes ago Up 12 minutes>8080/tcp,>8080/tcp tomcat8

But most commands seem to let you use the ‘friendly’ name you ascribed to the container. Running “docker inspect” will give you details about the container – including its IP address. I’ve found different images use different settings: some map to localhost on my box, some get an IP address within my DHCP range.

C:\docker\tomcat>docker inspect tomcat8 | grep IPAddress
"SecondaryIPAddresses": null,
"IPAddress": "",
"IPAddress": "",

Since this is an image that maps to localhost on my box, I need the lisa.rushworth.us hostname to resolve to my laptop’s IP address. For simplicity, I did this by editing the c:\windows\system32\drivers\etc\hosts file.

Shell into the container:

docker exec -it tomcat8 bash

Update your packages and install the kerberos client utilities:

root@4e06b32e1ca8:/usr/local/tomcat/conf# apt-get update
root@4e06b32e1ca8:/usr/local/tomcat/conf# apt-get install krb5-user

Then test that your keytab is working:

root@4e06b32e1ca8:/usr/local/tomcat/conf# kinit -k -t ./lisa.rushworth.us.keytab HTTP/lisa.rushworth.us@RUSHWORTH.US
root@4e06b32e1ca8:/usr/local/tomcat/conf# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: HTTP/lisa.rushworth.us@RUSHWORTH.US

Valid starting Expires Service principal
07/08/2017 18:27:38 07/09/2017 04:27:38 krbtgt/RUSHWORTH.US@RUSHWORTH.US
renew until 07/09/2017 18:27:38

Assuming you don’t get errors authenticating using the Kerberos client utilities, try accessing the TomCat site. I’ve added a testAuth.jsp file to the examples webapp – it shows the logon method, user name, and what roles they have:

09-Jul-2017 15:42:55.734 FINE [http-apr-8080-exec-1] org.apache.catalina.authenticator.SpnegoAuthenticator.authenticate Unable to login as the service principal
java.security.PrivilegedActionException: GSSException: Defective token detected (Mechanism level: GSSHeader did not find the right tag)

Verify that your SPN is set to the same name being used to access the site. I’m not sure why the configured service principal name doesn’t supersede the user-entered hostname. But I got nothing but auth failures until I actually entered the hostname into my hosts file and used an address that matches the service principal name.

Kerberos Authentication and LDAP Authorization In Apache

I’ve been authentcating users of Apache web sites against Active Directory using Kerberos for some time now. Installed krb5-workstation and mod_auth_kerb, configured /etc/krb5.conf for my specific domain, and added some config to the Directory section of the Apache config. Great if you just require valid-user (or require valid-user and then turn around and do some authorization within your web code using something like php_auth_user). Not so great, though, for restricting access to the site outside of web code. And I really didn’t want to code in an authorization function when my web server should be able to do that for me.

I FINALLY got kerberos authentication working in Apache with an LDAP authorization component. Turns out the  mod_auth_kerb version 5.1 that was available from the Yum repository is terribly buggy  – like not usable in this instance buggy. KrbLocalUserMapping did not consistently remove the realm component. I’d hit a site and it would know who I am, click a link and come across as me@REALM.TLD and get access denied errors, click refresh and get in because it knew I was me again. Or not. More than 50% failure rate.I built the 5.4 version from http://modauthkerb.sourceforge.net/ and haven’t had a problem since.

I’m authenticating to Active Directory using the Kerberos module then authorizing against a group housed in an external LDAP directory. You can totally point your LDAP config toward Active Directory & use AD groups instead:

AuthType Kerberos
AuthName “Kerberos AD Test”
KrbAuthoritative off
KrbMethodNegotiate on
KrbMethodK5Passwd on
KrbServiceName HTTP/this.isyour.url.tld@REALM.TLD
KrbAuthRealms REALM.TLD
KrbLocalUserMapping On
Krb5Keytab /path/to/keytabs/keytab.file

AuthBasicAuthoritative On
AuthBasicProvider ldap
AuthLDAPURL “ldaps://ldap.directory.tld/o=BaseDN?uid?sub?(&(cn=*))”

AuthLDAPGroupAttribute uniqueMember
AuthLDAPGroupAttributeIsDN on
require ldap-group cn=Website Test,ou=groups,o=BaseDN


WooHoo! I hit the site from my domain-member computer, it knows I am LisaR. It then turns around and finds an LDAP user matching uid=LisaR and grabs the user’s fully qualified DN (because AuthLDAPGroupAttributesIsDN is ‘on’ here … if you are using just uids in your member list, that would be off). It then verifies that the fully qualified DN is a member of the Website Test group.

Now I’m trying to figure out how to let the user log in without supplying a realm (not everyone’s in the domain … and they need to be able to log in too. Works fine right now, provided they input their username as uid@REALM.TLD).