trusts: support subdomains in a forest

Add IPA CLI to manage trust domains.

ipa trust-fetch-domains <trust>      -- fetch list of subdomains from AD side and add new ones to IPA
ipa trustdomain-find <trust>         -- show all available domains
ipa trustdomain-del <trust> <domain> -- remove domain from IPA view about <trust>
ipa trustdomain-enable <trust> <domain> -- allow users from trusted domain to access resources in IPA
ipa trustdomain-disable <trust> <domain> -- disable access to resources in IPA from trusted domain

By default all discovered trust domains are allowed to access IPA resources

IPA KDC needs also information for authentication paths to subdomains in case they
are not hierarchical under AD forest trust root. This information is managed via capaths
section in krb5.conf. SSSD should be able to generate it once
ticket https://fedorahosted.org/sssd/ticket/2093 is resolved.

part of https://fedorahosted.org/freeipa/ticket/3909

ipaserver/dcerpc.py

@@ -1002,6 +1002,60 @@ class TrustDomainInstance(object):
             return True
         return False
 
+def fetch_domains(api, mydomain, trustdomain):
+    trust_flags = dict(
+                NETR_TRUST_FLAG_IN_FOREST = 0x00000001,
+                NETR_TRUST_FLAG_OUTBOUND  = 0x00000002,
+                NETR_TRUST_FLAG_TREEROOT  = 0x00000004,
+                NETR_TRUST_FLAG_PRIMARY   = 0x00000008,
+                NETR_TRUST_FLAG_NATIVE    = 0x00000010,
+                NETR_TRUST_FLAG_INBOUND   = 0x00000020,
+                NETR_TRUST_FLAG_MIT_KRB5  = 0x00000080,
+                NETR_TRUST_FLAG_AES       = 0x00000100)
+
+    trust_attributes = dict(
+                NETR_TRUST_ATTRIBUTE_NON_TRANSITIVE     = 0x00000001,
+                NETR_TRUST_ATTRIBUTE_UPLEVEL_ONLY       = 0x00000002,
+                NETR_TRUST_ATTRIBUTE_QUARANTINED_DOMAIN = 0x00000004,
+                NETR_TRUST_ATTRIBUTE_FOREST_TRANSITIVE  = 0x00000008,
+                NETR_TRUST_ATTRIBUTE_CROSS_ORGANIZATION = 0x00000010,
+                NETR_TRUST_ATTRIBUTE_WITHIN_FOREST      = 0x00000020,
+                NETR_TRUST_ATTRIBUTE_TREAT_AS_EXTERNAL  = 0x00000040)
+
+    domval = DomainValidator(api)
+    (ccache_name, principal) = domval.kinit_as_http(trustdomain)
+    if ccache_name:
+        with installutils.private_ccache(path=ccache_name):
+            td = TrustDomainInstance('')
+            td.parm.set('workgroup', mydomain)
+            td.creds = credentials.Credentials()
+            td.creds.set_kerberos_state(credentials.MUST_USE_KERBEROS)
+            td.creds.guess(td.parm)
+            netrc = net.Net(creds=td.creds, lp=td.parm)
+            try:
+                result = netrc.finddc(domain=trustdomain, flags=nbt.NBT_SERVER_LDAP | nbt.NBT_SERVER_DS)
+            except RuntimeError, e:
+                raise assess_dcerpc_exception(message=str(e))
+            if not result:
+                return None
+            td.retrieve(unicode(result.pdc_dns_name))
+
+            netr_pipe = netlogon.netlogon(td.binding, td.parm, td.creds)
+            domains = netr_pipe.netr_DsrEnumerateDomainTrusts(td.binding, 1)
+
+            result = []
+            for t in domains.array:
+                if ((t.trust_attributes & trust_attributes['NETR_TRUST_ATTRIBUTE_WITHIN_FOREST']) and
+                    (t.trust_flags & trust_flags['NETR_TRUST_FLAG_IN_FOREST'])):
+                    res = dict()
+                    res['cn'] = unicode(t.dns_name)
+                    res['ipantflatname'] = unicode(t.netbios_name)
+                    res['ipanttrusteddomainsid'] = unicode(t.sid)
+                    res['ipanttrustpartner'] = res['cn']
+                    result.append(res)
+            return result
+
+
 class TrustDomainJoins(object):
     def __init__(self, api):
         self.api = api