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diff --git a/google/api_core/client_options.py b/google/api_core/client_options.py
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+# Copyright 2019 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.
+
+"""Client options class.
+
+Client options provide a consistent interface for user options to be defined
+across clients.
+
+You can pass a client options object to a client.
+
+.. code-block:: python
+
+    from google.api_core.client_options import ClientOptions
+    from google.cloud.vision_v1 import ImageAnnotatorClient
+
+    def get_client_cert():
+        # code to load client certificate and private key.
+        return client_cert_bytes, client_private_key_bytes
+
+    options = ClientOptions(api_endpoint="foo.googleapis.com",
+        client_cert_source=get_client_cert)
+
+    client = ImageAnnotatorClient(client_options=options)
+
+You can also pass a mapping object.
+
+.. code-block:: python
+
+    from google.cloud.vision_v1 import ImageAnnotatorClient
+
+    client = ImageAnnotatorClient(
+        client_options={
+            "api_endpoint": "foo.googleapis.com",
+            "client_cert_source" : get_client_cert
+        })
+
+
+"""
+
+
+class ClientOptions(object):
+    """Client Options used to set options on clients.
+
+    Args:
+        api_endpoint (Optional[str]): The desired API endpoint, e.g.,
+            compute.googleapis.com
+        client_cert_source (Optional[Callable[[], (bytes, bytes)]]): A callback
+            which returns client certificate bytes and private key bytes both in
+            PEM format. ``client_cert_source`` and ``client_encrypted_cert_source``
+            are mutually exclusive.
+        client_encrypted_cert_source (Optional[Callable[[], (str, str, bytes)]]):
+            A callback which returns client certificate file path, encrypted
+            private key file path, and the passphrase bytes.``client_cert_source``
+            and ``client_encrypted_cert_source`` are mutually exclusive.
+        quota_project_id (Optional[str]): A project name that a client's
+            quota belongs to.
+        credentials_file (Optional[str]): A path to a file storing credentials.
+        scopes (Optional[Sequence[str]]): OAuth access token override scopes.
+
+    Raises:
+        ValueError: If both ``client_cert_source`` and ``client_encrypted_cert_source``
+            are provided.
+    """
+
+    def __init__(
+        self,
+        api_endpoint=None,
+        client_cert_source=None,
+        client_encrypted_cert_source=None,
+        quota_project_id=None,
+        credentials_file=None,
+        scopes=None,
+    ):
+        if client_cert_source and client_encrypted_cert_source:
+            raise ValueError(
+                "client_cert_source and client_encrypted_cert_source are mutually exclusive"
+            )
+        self.api_endpoint = api_endpoint
+        self.client_cert_source = client_cert_source
+        self.client_encrypted_cert_source = client_encrypted_cert_source
+        self.quota_project_id = quota_project_id
+        self.credentials_file = credentials_file
+        self.scopes = scopes
+
+    def __repr__(self):
+        return "ClientOptions: " + repr(self.__dict__)
+
+
+def from_dict(options):
+    """Construct a client options object from a mapping object.
+
+    Args:
+        options (collections.abc.Mapping): A mapping object with client options.
+            See the docstring for ClientOptions for details on valid arguments.
+    """
+
+    client_options = ClientOptions()
+
+    for key, value in options.items():
+        if hasattr(client_options, key):
+            setattr(client_options, key, value)
+        else:
+            raise ValueError("ClientOptions does not accept an option '" + key + "'")
+
+    return client_options