Provide Kerberos over HTTP (MS-KKDCP)

Add integration of python-kdcproxy into FreeIPA to support the MS
Kerberos KDC proxy protocol (MS-KKDCP), to allow KDC and KPASSWD
client requests over HTTP and HTTPS.

- freeipa-server now depends on python-kdcproxy >= 0.3. All kdcproxy
  dependencies are already satisfied.
- The service's state is configured in cn=KDC,cn=$FQDN,cn=masters,cn=ipa,
  cn=etc,$SUFFIX. It's enabled, when ipaConfigString=kdcProxyEnabled is
  present.
- The installers and update create a new Apache config file
  /etc/ipa/kdcproxy/ipa-kdc-proxy.conf that mounts a WSGI app on
  /KdcProxy. The app is run inside its own WSGI daemon group with
  a different uid and gid than the webui.
- A ExecStartPre script in httpd.service symlinks the config file to
  /etc/httpd/conf.d/ iff ipaConfigString=kdcProxyEnabled is present.
- The httpd.service also sets KDCPROXY_CONFIG=/etc/ipa/kdcproxy.conf,
  so that an existing config is not used. SetEnv from Apache config does
  not work here, because it doesn't set an OS env var.
- python-kdcproxy is configured to *not* use DNS SRV lookups. The
  location of KDC and KPASSWD servers are read from /etc/krb5.conf.
- The state of the service can be modified with two ldif files for
  ipa-ldap-updater. No CLI script is offered yet.

https://www.freeipa.org/page/V4/KDC_Proxy

https://fedorahosted.org/freeipa/ticket/4801

Reviewed-By: Nathaniel McCallum <npmccallum@redhat.com>
Reviewed-By: Simo Sorce <ssorce@redhat.com>

ipaplatform/base/paths.py

@@ -49,6 +49,8 @@ class BasePathNamespace(object):
     ALIAS_CACERT_ASC = "/etc/httpd/alias/cacert.asc"
     ALIAS_PWDFILE_TXT = "/etc/httpd/alias/pwdfile.txt"
     HTTPD_CONF_D_DIR = "/etc/httpd/conf.d/"
+    HTTPD_IPA_KDCPROXY_CONF = "/etc/ipa/kdcproxy/ipa-kdc-proxy.conf"
+    HTTPD_IPA_KDCPROXY_CONF_SYMLINK = "/etc/httpd/conf.d/ipa-kdc-proxy.conf"
     HTTPD_IPA_PKI_PROXY_CONF = "/etc/httpd/conf.d/ipa-pki-proxy.conf"
     HTTPD_IPA_REWRITE_CONF = "/etc/httpd/conf.d/ipa-rewrite.conf"
     HTTPD_IPA_CONF = "/etc/httpd/conf.d/ipa.conf"
@@ -342,7 +344,7 @@ class BasePathNamespace(object):
     DB2LDIF = '/usr/sbin/db2ldif'
     BAK2DB = '/usr/sbin/bak2db'
     DB2BAK = '/usr/sbin/db2bak'
-
+    KDCPROXY_CONFIG = '/etc/ipa/kdcproxy/kdcproxy.conf'
 
 
 path_namespace = BasePathNamespace