Hello, since May 1st I'm a new Red Hat employee and developer with the FreeIPA team. Some of you may already recognize my name from my contributions to CPython core, Python security and TLS/SSL improvements, or a couple of PEPs. I'm very glad that I can now work on Open Source as a full time job. I haven't had any dealings with FreeIPA before and just rudimentary experience with LDAP and Kerberos as a developer. Over the past two weeks I have been digging through FreeIPA sources, read docs and played with its services. I'm slowly starting to grasp the building blocks.
I was put in charge of MS-KKDCP integration into FreeIPA 4.2 . The task is small and isolated enough for a new contributor. KKDCP stands for Kerberos KDC proxy protocol. It was developed by Microsoft to tunnel KDC requests over HTTPS. It's useful for firewalled environments where 88/TCP+UDP are blocked and only 80/TCP + 443/TCP are available. With KKDCP the client side wraps each Kerberos request in an additional ASN.1 sequence and sends it as POST request to a proxy. The proxy unpacks the request, forwards it to a KDC and returns its reply to the client. MIT krb5 supports  KKDCP since 1.13, Fedora has backports for 1.12. Nathaniel McCallum has written  a proxy server as WSGI app. I'm working on improvements and integration of the WSGI app into FreeIPA. Yesterday several bug fixes already landed in kdcproxy. The integration into FreeIPA is the tricky part for me. I'm not familiar enough with FreeIPA yet to understand possible implications, so I need your guidance. I already got some feedback from several people (Dmitri, Nathan, Nathaniel, Martin, Martin2, Petr, Alexander...). Here is what I have so far: 1) The FreeIPA webui already depends on Apache and mod_wsgi. KDC proxy will run from the same Apache HTTPD instance but it will use a different mod_wsgi daemon configuration. A second WSGI daemon is easily configured and allows us to tune the daemon for KDC proxy's needs. FreeIPA is mounted at /ipa, KDC Proxy will be available at /KdcProxy or /kdc. 2) For now we are not going to introduce a separate package freeipa-server-kdcproxy. freeipa-server will depend on python-kdcproxy and install all configuration files. Therefore the entry point /KdcProxy is always configured 3) An administrator must be able to enable/disable the new feature. The state of the switch will be read when Apache is started or reloaded. The feature must be configurable for each replica, too. A WSGI wrapper will read the setting from ipaConfigString=enabledService in cn=KDCPROXY,cn=$FQDN,cn=masters,cn=ipa,cn=etc. When the feature is disabled, it will reply with 404 Not Found error. 4) In order to read the state of the switch, the WSGI script needs to be able to connect to LDAP. I can use Apache's / FreeIPA webui's keytab to get a ticket for GSSAPI bind. However Apache has no permission to read ipaConfigStrings in the masters subtree. A new role/permission and ACI is required here. 5) python-kdcproxy can read its configuration from multiple places. For performance reasons we don't want DNS lookups. Therefore our proxy instance will only use libkrb5.so to read a list of KDCs, kpasswd and admin servers from /etc/krb5.conf. Open questions / issues ----------------------- For 3) and 4) the Apache HTTP principal must be able to read or at least compare the state of the switch. The ACIs in the masters tree forbid any access to ipaConfigString entries except for principals with 'System: Read IPA Masters' permission. Martin Basti and Petr Spacek have suggested that I introduce a new permission for the task. I haven't figured out how to configure and assign a new permission. Right now my experimental code uses this ACI: (targetfilter="(ipaConfigString=enabledService)")(targetattr="ipaConfigString")(version 3.0; acl "Compare enabledService access to masters"; allow(search, compare) userdn = "ldap:///all";) I found ipaserver.install.service.Service and SimpleServiceInstance in the FreeIPA sources. As far as I understand the use of the classes, they are used in the installers to configure service instances. However the kdcproxy service instance is going to be special. It has no 1:1 relation to a system service. Instead it shares a system service (Apache HTTPD) with the HttpInstance for FreeIPA's webui. AFAIK no other service instance has such a relation. Finally I haven't figured out the best way to configure the instance. An admin should be able to enable / disable KDC proxy. Should I write a script or a ipa plugin for the job? You can find my patch in my Github repos . The installer code is mostly untested, though. Please advice :) Christian  https://www.freeipa.org/page/V4/KDC_Proxy  http://web.mit.edu/kerberos/krb5-current/doc/admin/https.html  https://github.com/npmccallum/kdcproxy  https://github.com/tiran/freeipa/compare/master...kdcproxy2
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