Added preliminary Kerberos authentication support

certidude/auth.py

@@ -0,0 +1,60 @@
+
+import click
+import falcon
+import kerberos
+import os
+import re
+import socket
+
+# Vanilla Kerberos provides only username.
+# AD also embeds PAC (Privilege Attribute Certificate), which
+# is supposed to be sent via HTTP headers and it contains
+# the groups user is part of.
+# Even then we would have to manually look up the e-mail
+# address eg via LDAP, hence to keep things simple
+# we simply use Kerberos to authenticate.
+
+FQDN = socket.getaddrinfo(socket.gethostname(), 0, flags=socket.AI_CANONNAME)[0][3]
+
+if not os.getenv("KRB5_KTNAME"):
+    click.echo("Kerberos keytab not specified, set environment variable 'KRB5_KTNAME'", err=True)
+    exit(250)
+
+try:
+    principal = kerberos.getServerPrincipalDetails("HTTP", FQDN)
+except kerberos.KrbError as exc:
+    click.echo("Failed to initialize Kerberos, reason: %s" % exc, err=True)
+    exit(249)
+else:
+    click.echo("Kerberos enabled, service principal is HTTP/%s" % FQDN)
+
+def login_required(func):
+    def wrapped(resource, req, resp, *args, **kwargs):
+        authorization = req.get_header("Authorization")
+
+        if not authorization:
+            resp.append_header("WWW-Authenticate", "Negotiate")
+            raise falcon.HTTPUnauthorized("Unauthorized", "No Kerberos ticket offered?")
+
+        token = ''.join(authorization.split()[1:])
+
+        rc, context = kerberos.authGSSServerInit("HTTP@" + FQDN)
+        if rc != kerberos.AUTH_GSS_COMPLETE:
+            raise falcon.HTTPForbidden("Forbidden", "Kerberos ticket expired?")
+
+        rc = kerberos.authGSSServerStep(context, token)
+        kerberos_user = kerberos.authGSSServerUserName(context).split("@")
+
+        # References lost beyond this point! Results in
+        # ValueError: PyCapsule_SetPointer called with null pointer
+        kerberos.authGSSServerClean(context)
+
+        if rc == kerberos.AUTH_GSS_COMPLETE:
+            kwargs["user"] = kerberos_user
+            return func(resource, req, resp, *args, **kwargs)
+        elif rc == kerberos.AUTH_GSS_CONTINUE:
+            raise falcon.HTTPUnauthorized("Unauthorized", "Tried GSSAPI")
+        else:
+            raise falcon.HTTPForbidden("Forbidden", "Tried GSSAPI")
+
+    return wrapped