diff --git a/google/oauth2/sts.py b/google/oauth2/sts.py
new file mode 100644
index 0000000..ae3c014
--- /dev/null
+++ b/google/oauth2/sts.py
@@ -0,0 +1,155 @@
+# 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.
+
+"""OAuth 2.0 Token Exchange Spec.
+
+This module defines a token exchange utility based on the `OAuth 2.0 Token
+Exchange`_ spec. This will be mainly used to exchange external credentials
+for GCP access tokens in workload identity pools to access Google APIs.
+
+The implementation will support various types of client authentication as
+allowed in the spec.
+
+A deviation on the spec will be for additional Google specific options that
+cannot be easily mapped to parameters defined in the RFC.
+
+The returned dictionary response will be based on the `rfc8693 section 2.2.1`_
+spec JSON response.
+
+.. _OAuth 2.0 Token Exchange: https://tools.ietf.org/html/rfc8693
+.. _rfc8693 section 2.2.1: https://tools.ietf.org/html/rfc8693#section-2.2.1
+"""
+
+import json
+
+from six.moves import http_client
+from six.moves import urllib
+
+from google.oauth2 import utils
+
+
+_URLENCODED_HEADERS = {"Content-Type": "application/x-www-form-urlencoded"}
+
+
+class Client(utils.OAuthClientAuthHandler):
+    """Implements the OAuth 2.0 token exchange spec based on
+    https://tools.ietf.org/html/rfc8693.
+    """
+
+    def __init__(self, token_exchange_endpoint, client_authentication=None):
+        """Initializes an STS client instance.
+
+        Args:
+            token_exchange_endpoint (str): The token exchange endpoint.
+            client_authentication (Optional(google.oauth2.oauth2_utils.ClientAuthentication)):
+                The optional OAuth client authentication credentials if available.
+        """
+        super(Client, self).__init__(client_authentication)
+        self._token_exchange_endpoint = token_exchange_endpoint
+
+    def exchange_token(
+        self,
+        request,
+        grant_type,
+        subject_token,
+        subject_token_type,
+        resource=None,
+        audience=None,
+        scopes=None,
+        requested_token_type=None,
+        actor_token=None,
+        actor_token_type=None,
+        additional_options=None,
+        additional_headers=None,
+    ):
+        """Exchanges the provided token for another type of token based on the
+        rfc8693 spec.
+
+        Args:
+            request (google.auth.transport.Request): A callable used to make
+                HTTP requests.
+            grant_type (str): The OAuth 2.0 token exchange grant type.
+            subject_token (str): The OAuth 2.0 token exchange subject token.
+            subject_token_type (str): The OAuth 2.0 token exchange subject token type.
+            resource (Optional[str]): The optional OAuth 2.0 token exchange resource field.
+            audience (Optional[str]): The optional OAuth 2.0 token exchange audience field.
+            scopes (Optional[Sequence[str]]): The optional list of scopes to use.
+            requested_token_type (Optional[str]): The optional OAuth 2.0 token exchange requested
+                token type.
+            actor_token (Optional[str]): The optional OAuth 2.0 token exchange actor token.
+            actor_token_type (Optional[str]): The optional OAuth 2.0 token exchange actor token type.
+            additional_options (Optional[Mapping[str, str]]): The optional additional
+                non-standard Google specific options.
+            additional_headers (Optional[Mapping[str, str]]): The optional additional
+                headers to pass to the token exchange endpoint.
+
+        Returns:
+            Mapping[str, str]: The token exchange JSON-decoded response data containing
+                the requested token and its expiration time.
+
+        Raises:
+            google.auth.exceptions.OAuthError: If the token endpoint returned
+                an error.
+        """
+        # Initialize request headers.
+        headers = _URLENCODED_HEADERS.copy()
+        # Inject additional headers.
+        if additional_headers:
+            for k, v in dict(additional_headers).items():
+                headers[k] = v
+        # Initialize request body.
+        request_body = {
+            "grant_type": grant_type,
+            "resource": resource,
+            "audience": audience,
+            "scope": " ".join(scopes or []),
+            "requested_token_type": requested_token_type,
+            "subject_token": subject_token,
+            "subject_token_type": subject_token_type,
+            "actor_token": actor_token,
+            "actor_token_type": actor_token_type,
+            "options": None,
+        }
+        # Add additional non-standard options.
+        if additional_options:
+            request_body["options"] = urllib.parse.quote(json.dumps(additional_options))
+        # Remove empty fields in request body.
+        for k, v in dict(request_body).items():
+            if v is None or v == "":
+                del request_body[k]
+        # Apply OAuth client authentication.
+        self.apply_client_authentication_options(headers, request_body)
+
+        # Execute request.
+        response = request(
+            url=self._token_exchange_endpoint,
+            method="POST",
+            headers=headers,
+            body=urllib.parse.urlencode(request_body).encode("utf-8"),
+        )
+
+        response_body = (
+            response.data.decode("utf-8")
+            if hasattr(response.data, "decode")
+            else response.data
+        )
+
+        # If non-200 response received, translate to OAuthError exception.
+        if response.status != http_client.OK:
+            utils.handle_error_response(response_body)
+
+        response_data = json.loads(response_body)
+
+        # Return successful response.
+        return response_data
diff --git a/google/oauth2/utils.py b/google/oauth2/utils.py
new file mode 100644
index 0000000..efda796
--- /dev/null
+++ b/google/oauth2/utils.py
@@ -0,0 +1,171 @@
+# 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.
+
+"""OAuth 2.0 Utilities.
+
+This module provides implementations for various OAuth 2.0 utilities.
+This includes `OAuth error handling`_ and
+`Client authentication for OAuth flows`_.
+
+OAuth error handling
+--------------------
+This will define interfaces for handling OAuth related error responses as
+stated in `RFC 6749 section 5.2`_.
+This will include a common function to convert these HTTP error responses to a
+:class:`google.auth.exceptions.OAuthError` exception.
+
+
+Client authentication for OAuth flows
+-------------------------------------
+We introduce an interface for defining client authentication credentials based
+on `RFC 6749 section 2.3.1`_. This will expose the following
+capabilities:
+
+    * Ability to support basic authentication via request header.
+    * Ability to support bearer token authentication via request header.
+    * Ability to support client ID / secret authentication via request body.
+
+.. _RFC 6749 section 2.3.1: https://tools.ietf.org/html/rfc6749#section-2.3.1
+.. _RFC 6749 section 5.2: https://tools.ietf.org/html/rfc6749#section-5.2
+"""
+
+import abc
+import base64
+import enum
+import json
+
+import six
+
+from google.auth import exceptions
+
+
+# OAuth client authentication based on
+# https://tools.ietf.org/html/rfc6749#section-2.3.
+class ClientAuthType(enum.Enum):
+    basic = 1
+    request_body = 2
+
+
+class ClientAuthentication(object):
+    """Defines the client authentication credentials for basic and request-body
+    types based on https://tools.ietf.org/html/rfc6749#section-2.3.1.
+    """
+
+    def __init__(self, client_auth_type, client_id, client_secret=None):
+        """Instantiates a client authentication object containing the client ID
+        and secret credentials for basic and response-body auth.
+
+        Args:
+            client_auth_type (google.oauth2.oauth_utils.ClientAuthType): The
+                client authentication type.
+            client_id (str): The client ID.
+            client_secret (Optional[str]): The client secret.
+        """
+        self.client_auth_type = client_auth_type
+        self.client_id = client_id
+        self.client_secret = client_secret
+
+
+@six.add_metaclass(abc.ABCMeta)
+class OAuthClientAuthHandler(object):
+    """Abstract class for handling client authentication in OAuth-based
+    operations.
+    """
+
+    def __init__(self, client_authentication=None):
+        """Instantiates an OAuth client authentication handler.
+
+        Args:
+            client_authentication (Optional[google.oauth2.utils.ClientAuthentication]):
+                The OAuth client authentication credentials if available.
+        """
+        super(OAuthClientAuthHandler, self).__init__()
+        self._client_authentication = client_authentication
+
+    def apply_client_authentication_options(
+        self, headers, request_body=None, bearer_token=None
+    ):
+        """Applies client authentication on the OAuth request's headers or POST
+        body.
+
+        Args:
+            headers (Mapping[str, str]): The HTTP request header.
+            request_body (Optional[Mapping[str, str]): The HTTP request body
+                dictionary. For requests that do not support request body, this
+                is None and will be ignored.
+            bearer_token (Optional[str]): The optional bearer token.
+        """
+        # Inject authenticated header.
+        self._inject_authenticated_headers(headers, bearer_token)
+        # Inject authenticated request body.
+        if bearer_token is None:
+            self._inject_authenticated_request_body(request_body)
+
+    def _inject_authenticated_headers(self, headers, bearer_token=None):
+        if bearer_token is not None:
+            headers["Authorization"] = "Bearer %s" % bearer_token
+        elif (
+            self._client_authentication is not None
+            and self._client_authentication.client_auth_type is ClientAuthType.basic
+        ):
+            username = self._client_authentication.client_id
+            password = self._client_authentication.client_secret or ""
+
+            credentials = base64.b64encode(
+                ("%s:%s" % (username, password)).encode()
+            ).decode()
+            headers["Authorization"] = "Basic %s" % credentials
+
+    def _inject_authenticated_request_body(self, request_body):
+        if (
+            self._client_authentication is not None
+            and self._client_authentication.client_auth_type
+            is ClientAuthType.request_body
+        ):
+            if request_body is None:
+                raise exceptions.OAuthError(
+                    "HTTP request does not support request-body"
+                )
+            else:
+                request_body["client_id"] = self._client_authentication.client_id
+                request_body["client_secret"] = (
+                    self._client_authentication.client_secret or ""
+                )
+
+
+def handle_error_response(response_body):
+    """Translates an error response from an OAuth operation into an
+    OAuthError exception.
+
+    Args:
+        response_body (str): The decoded response data.
+
+    Raises:
+        google.auth.exceptions.OAuthError
+    """
+    try:
+        error_components = []
+        error_data = json.loads(response_body)
+
+        error_components.append("Error code {}".format(error_data["error"]))
+        if "error_description" in error_data:
+            error_components.append(": {}".format(error_data["error_description"]))
+        if "error_uri" in error_data:
+            error_components.append(" - {}".format(error_data["error_uri"]))
+        error_details = "".join(error_components)
+    # If no details could be extracted, use the response data.
+    except (KeyError, ValueError):
+        error_details = response_body
+
+    raise exceptions.OAuthError(error_details, response_body)