1 files changed, 105 insertions, 0 deletions
diff --git a/google/auth/transport/mtls.py b/google/auth/transport/mtls.py
new file mode 100644
index 0000000..b40bfbe
--- /dev/null
+++ b/google/auth/transport/mtls.py
@@ -0,0 +1,105 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Utilites for mutual TLS."""
+
+import six
+
+from google.auth import exceptions
+from google.auth.transport import _mtls_helper
+
+
+def has_default_client_cert_source():
+    """Check if default client SSL credentials exists on the device.
+
+    Returns:
+        bool: indicating if the default client cert source exists.
+    """
+    metadata_path = _mtls_helper._check_dca_metadata_path(
+        _mtls_helper.CONTEXT_AWARE_METADATA_PATH
+    )
+    return metadata_path is not None
+
+
+def default_client_cert_source():
+    """Get a callback which returns the default client SSL credentials.
+
+    Returns:
+        Callable[[], [bytes, bytes]]: A callback which returns the default
+            client certificate bytes and private key bytes, both in PEM format.
+
+    Raises:
+        google.auth.exceptions.DefaultClientCertSourceError: If the default
+            client SSL credentials don't exist or are malformed.
+    """
+    if not has_default_client_cert_source():
+        raise exceptions.MutualTLSChannelError(
+            "Default client cert source doesn't exist"
+        )
+
+    def callback():
+        try:
+            _, cert_bytes, key_bytes = _mtls_helper.get_client_cert_and_key()
+        except (OSError, RuntimeError, ValueError) as caught_exc:
+            new_exc = exceptions.MutualTLSChannelError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
+
+        return cert_bytes, key_bytes
+
+    return callback
+
+
+def default_client_encrypted_cert_source(cert_path, key_path):
+    """Get a callback which returns the default encrpyted client SSL credentials.
+
+    Args:
+        cert_path (str): The cert file path. The default client certificate will
+            be written to this file when the returned callback is called.
+        key_path (str): The key file path. The default encrypted client key will
+            be written to this file when the returned callback is called.
+
+    Returns:
+        Callable[[], [str, str, bytes]]: A callback which generates the default
+            client certificate, encrpyted private key and passphrase. It writes
+            the certificate and private key into the cert_path and key_path, and
+            returns the cert_path, key_path and passphrase bytes.
+
+    Raises:
+        google.auth.exceptions.DefaultClientCertSourceError: If any problem
+            occurs when loading or saving the client certificate and key.
+    """
+    if not has_default_client_cert_source():
+        raise exceptions.MutualTLSChannelError(
+            "Default client encrypted cert source doesn't exist"
+        )
+
+    def callback():
+        try:
+            (
+                _,
+                cert_bytes,
+                key_bytes,
+                passphrase_bytes,
+            ) = _mtls_helper.get_client_ssl_credentials(generate_encrypted_key=True)
+            with open(cert_path, "wb") as cert_file:
+                cert_file.write(cert_bytes)
+            with open(key_path, "wb") as key_file:
+                key_file.write(key_bytes)
+        except (exceptions.ClientCertError, OSError) as caught_exc:
+            new_exc = exceptions.MutualTLSChannelError(caught_exc)
+            six.raise_from(new_exc, caught_exc)
+
+        return cert_path, key_path, passphrase_bytes
+
+    return callback