Expose set_purpose on X509Store to allow verify_certificate with purpose

src/OpenSSL/crypto.py

@@ -33,6 +33,7 @@
     "X509Req",
     "X509",
     "X509StoreFlags",
+    "X509StorePurposes",
     "X509Store",
     "X509StoreContextError",
     "X509StoreContext",
@@ -1583,6 +1584,28 @@ class X509StoreFlags:
     CHECK_SS_SIGNATURE = _lib.X509_V_FLAG_CHECK_SS_SIGNATURE
 
 
+class X509StorePurposes:
+    """
+    Flags for X509 verification, used to change the behavior of
+    :class:`X509Store`.
+
+    See `OpenSSL check purpose`_ for details.
+
+    .. _OpenSSL check purpose:
+        https://www.openssl.org/docs/manmaster/man3/X509_check_purpose.html
+    """
+
+    X509_PURPOSE_SSL_CLIENT = _lib.X509_PURPOSE_SSL_CLIENT
+    X509_PURPOSE_SSL_SERVER = _lib.X509_PURPOSE_SSL_SERVER
+    X509_PURPOSE_NS_SSL_SERVER = _lib.X509_PURPOSE_NS_SSL_SERVER
+    X509_PURPOSE_SMIME_SIGN = _lib.X509_PURPOSE_SMIME_SIGN
+    X509_PURPOSE_SMIME_ENCRYPT = _lib.X509_PURPOSE_SMIME_ENCRYPT
+    X509_PURPOSE_CRL_SIGN = _lib.X509_PURPOSE_CRL_SIGN
+    X509_PURPOSE_ANY = _lib.X509_PURPOSE_ANY
+    X509_PURPOSE_OCSP_HELPER = _lib.X509_PURPOSE_OCSP_HELPER
+    X509_PURPOSE_TIMESTAMP_SIGN = _lib.X509_PURPOSE_TIMESTAMP_SIGN
+
+
 class X509Store:
     """
     An X.509 store.
@@ -1687,6 +1710,22 @@ def set_time(self, vfy_time):
         )
         _openssl_assert(_lib.X509_STORE_set1_param(self._store, param) != 0)
 
+    def set_purpose(self, purpose):
+        """
+        Set purpose of this store.
+
+        .. versionadded:: 22.1.0
+
+        :param int flags: The verification flags to set on this store.
+            See :class:`X509StorePurposes` for available constants.
+        :return: ``None`` if the verification flags were successfully set.
+        """
+
+        param = _lib.X509_VERIFY_PARAM_new()
+        param = _ffi.gc(param, _lib.X509_VERIFY_PARAM_free)
+        _lib.X509_VERIFY_PARAM_set_purpose(param, purpose)
+        _openssl_assert(_lib.X509_STORE_set1_param(self._store, param) != 0)
+
     def load_locations(self, cafile, capath=None):
         """
         Let X509Store know where we can find trusted certificates for the

tests/test_crypto.py

@@ -26,6 +26,7 @@
 from OpenSSL.crypto import (
     X509Store,
     X509StoreFlags,
+    X509StorePurposes,
     X509StoreContext,
     X509StoreContextError,
 )
@@ -3528,6 +3529,7 @@ class TestCRL:
     intermediate_server_key = load_privatekey(
         FILETYPE_PEM, intermediate_server_key_pem
     )
+    server_cert = load_certificate(FILETYPE_PEM, server_cert_pem)
 
     def test_construction(self):
         """
@@ -3835,6 +3837,32 @@ def test_verify_with_revoked(self):
             store_ctx.verify_certificate()
         assert err.value.args[0][2] == "certificate revoked"
 
+    def test_verify_with_correct_purpose(self):
+        store = X509Store()
+        store.add_cert(self.root_cert)
+        store.add_cert(self.intermediate_cert)
+        store.set_purpose(X509StorePurposes.X509_PURPOSE_SSL_SERVER)
+
+        store_ctx = X509StoreContext(store, self.server_cert)
+        store_ctx.verify_certificate()
+
+        # The intermediate server certificate has no EKU and so it is fit
+        # for any purpose
+        store_ctx = X509StoreContext(store, self.intermediate_server_cert)
+        store_ctx.verify_certificate()
+
+    def test_verify_with_incorrect_purpose(self):
+        store = X509Store()
+        store.add_cert(self.root_cert)
+        store.add_cert(self.intermediate_cert)
+        store.set_purpose(X509StorePurposes.X509_PURPOSE_SSL_CLIENT)
+
+        store_ctx = X509StoreContext(store, self.server_cert)
+        with pytest.raises(X509StoreContextError) as err:
+            store_ctx.verify_certificate()
+
+        assert err.value.args[0][2] == "unsupported certificate purpose"
+
     def test_verify_with_missing_crl(self):
         """
         `verify_certificate` raises error when an intermediate certificate's