add extendedkeyusage extension
diff --git a/docs/x509.rst b/docs/x509.rst
index d8fce97..af24944 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -475,6 +475,15 @@
subordinate CA, but the subordinate CA is not allowed to create
subordinates with ``ca`` set to true.
+.. class:: ExtendedKeyUsage
+
+ .. versionadded:: 0.9
+
+ This extension indicates one or more purposes for which the certified
+ public key may be used, in addition to or in place of the basic
+ purposes indicated in the key usage extension. The object is
+ iterable to obtain the list of :ref:`extended key usage OIDs <eku_oids>`.
+
Object Identifiers
~~~~~~~~~~~~~~~~~~
@@ -633,6 +642,8 @@
Corresponds to the dotted string ``"2.16.840.1.101.3.4.3.2"``. This is
a SHA256 digest signed by a DSA key.
+.. _eku_oids:
+
Extended Key Usage OIDs
~~~~~~~~~~~~~~~~~~~~~~~