diff --git a/oauth2client/appengine.py b/oauth2client/appengine.py
index b463d4a..e90a4c6 100644
--- a/oauth2client/appengine.py
+++ b/oauth2client/appengine.py
@@ -164,6 +164,7 @@ class AppAssertionCredentials(AssertionCredentials):
           unspecified, the default service account for the app is used.
     """
     self.scope = util.scopes_to_string(scope)
+    self._kwargs = kwargs
     self.service_account_id = kwargs.get('service_account_id', None)
 
     # Assertion type is no longer used, but still in the parent class signature.
@@ -196,6 +197,12 @@ class AppAssertionCredentials(AssertionCredentials):
       raise AccessTokenRefreshError(str(e))
     self.access_token = token
 
+  def create_scoped_required(self):
+    return not self.scope
+
+  def create_scoped(self, scopes):
+    return AppAssertionCredentials(scopes, **self._kwargs)
+
 
 class FlowProperty(db.Property):
   """App Engine datastore Property for Flow.
diff --git a/oauth2client/client.py b/oauth2client/client.py
index 99873e2..6279d7a 100644
--- a/oauth2client/client.py
+++ b/oauth2client/client.py
@@ -66,6 +66,14 @@ OOB_CALLBACK_URN = 'urn:ietf:wg:oauth:2.0:oob'
 # Google Data client libraries may need to set this to [401, 403].
 REFRESH_STATUS_CODES = [401]
 
+# The value representing user credentials.
+AUTHORIZED_USER = 'authorized_user'
+
+# The value representing service account credentials.
+SERVICE_ACCOUNT = 'service_account'
+
+# The environment variable pointing the file with local Default Credentials.
+GOOGLE_CREDENTIALS_DEFAULT = 'GOOGLE_CREDENTIALS_DEFAULT'
 
 class Error(Exception):
   """Base error for this module."""
@@ -99,6 +107,10 @@ class NonAsciiHeaderError(Error):
   """Header names and values must be ASCII strings."""
 
 
+class DefaultCredentialsError(Error):
+  """Error retrieving the Default Credentials."""
+
+
 def _abstract():
   raise NotImplementedError('You need to override this function')
 
@@ -126,7 +138,7 @@ class Credentials(object):
   an HTTP transport.
 
   Subclasses must also specify a classmethod named 'from_json' that takes a JSON
-  string as input and returns an instaniated Credentials object.
+  string as input and returns an instantiated Credentials object.
   """
 
   NON_SERIALIZED_MEMBERS = ['store']
@@ -375,7 +387,7 @@ def _update_query_params(uri, params):
     The same URI but with the new query parameters added.
   """
   parts = list(urlparse.urlparse(uri))
-  query_params = dict(parse_qsl(parts[4])) # 4 is the index of the query part
+  query_params = dict(parse_qsl(parts[4]))  # 4 is the index of the query part
   query_params.update(params)
   parts[4] = urllib.urlencode(query_params)
   return urlparse.urlunparse(parts)
@@ -587,6 +599,20 @@ class OAuth2Credentials(Credentials):
       return True
     return False
 
+  def get_access_token(self, http=None):
+    """Return the access token.
+
+    If the token does not exist, get one.
+    If the token expired, refresh it.
+    """
+    if self.access_token and not self.access_token_expired:
+      return self.access_token
+    else:
+      if not http:
+        http = httplib2.Http()
+      self.refresh(http)
+      return self.access_token
+
   def set_store(self, store):
     """Set the Storage for the credential.
 
@@ -820,7 +846,303 @@ class AccessTokenCredentials(OAuth2Credentials):
     self._do_revoke(http_request, self.access_token)
 
 
-class AssertionCredentials(OAuth2Credentials):
+_env_name = None
+
+
+def _get_environment(urllib2_urlopen=None):
+  """Detect the environment the code is being run on."""
+
+  global _env_name
+  
+  if _env_name:
+    return _env_name
+
+  server_software = os.environ.get('SERVER_SOFTWARE', '')
+  if server_software.startswith('Google App Engine/'):
+    _env_name = 'GAE_PRODUCTION'
+  elif server_software.startswith('Development/'):
+    _env_name = 'GAE_LOCAL'
+  else:
+    import urllib2
+    try:
+      if urllib2_urlopen is None:
+        urllib2_urlopen = urllib2.urlopen
+      response = urllib2_urlopen('http://metadata.google.internal')
+      if any('Metadata-Flavor: Google' in h for h in response.info().headers):
+        _env_name = 'GCE_PRODUCTION'
+      else:
+        _env_name = 'UNKNOWN'
+    except urllib2.URLError:
+      _env_name = 'UNKNOWN'
+
+  return _env_name
+
+
+class GoogleCredentials(OAuth2Credentials):
+  """Default credentials for use in calling Google APIs.
+  
+  The Default Credentials are being constructed as a function of the environment
+  where the code is being run. More details can be found on this page:
+  https://developers.google.com/accounts/docs/default-credentials
+
+  Here is an example of how to use the Default Credentials for a service that
+  requires authentication:
+
+  <code>
+  from googleapiclient.discovery import build
+  from oauth2client.client import GoogleCredentials
+
+  PROJECT = 'bamboo-machine-422'  # replace this with one of your projects
+  ZONE = 'us-central1-a'          # replace this with the zone you care about
+
+  service = build('compute', 'v1', credentials=GoogleCredentials.get_default())
+
+  request = service.instances().list(project=PROJECT, zone=ZONE)
+  response = request.execute()
+
+  print response
+  </code>
+
+  A service that does not require authentication does not need credentials
+  to be passed in:
+
+  <code>
+  from googleapiclient.discovery import build
+
+  service = build('discovery', 'v1')
+
+  request = service.apis().list()
+  response = request.execute()
+
+  print response
+  </code>
+  """
+
+  def __init__(self, access_token, client_id, client_secret, refresh_token,
+               token_expiry, token_uri, user_agent,
+               revoke_uri=GOOGLE_REVOKE_URI):
+    """Create an instance of GoogleCredentials.
+
+    This constructor is not usually called by the user, instead
+    GoogleCredentials objects are instantiated by
+    GoogleCredentials.from_stream() or GoogleCredentials.get_default().
+
+    Args:
+      access_token: string, access token.
+      client_id: string, client identifier.
+      client_secret: string, client secret.
+      refresh_token: string, refresh token.
+      token_expiry: datetime, when the access_token expires.
+      token_uri: string, URI of token endpoint.
+      user_agent: string, The HTTP User-Agent to provide for this application.
+      revoke_uri: string, URI for revoke endpoint.
+        Defaults to GOOGLE_REVOKE_URI; a token can't be revoked if this is None.
+    """
+    super(GoogleCredentials, self).__init__(
+        access_token, client_id, client_secret, refresh_token, token_expiry,
+        token_uri, user_agent, revoke_uri=revoke_uri)
+    
+  def create_scoped_required(self):
+    """Whether this Credentials object is scopeless.
+    
+    create_scoped(scopes) method needs to be called in order to create
+    a Credentials object for API calls.
+    """
+    return False
+  
+  def create_scoped(self, scopes):
+    """Create a Credentials object for the given scopes.
+    
+    The Credentials type is preserved.
+    """ 
+    return self
+
+  @staticmethod
+  def get_default():
+    """Get the Default Credentials for the current environment.
+
+    Exceptions:
+      DefaultCredentialsError: raised when the credentials fail to be retrieved.
+    """
+
+    _env_name = _get_environment()
+
+    if _env_name in ('GAE_PRODUCTION', 'GAE_LOCAL'):
+      # if we are running inside Google App Engine
+      # there is no need to look for credentials in local files
+      default_credential_filename = None
+      well_known_file = None
+    else:
+      default_credential_filename = _get_environment_variable_file()
+      well_known_file = _get_well_known_file()
+
+    if default_credential_filename:
+      try:
+        return _get_default_credential_from_file(default_credential_filename)
+      except (DefaultCredentialsError, ValueError) as error:
+        extra_help = (' (pointed to by ' + GOOGLE_CREDENTIALS_DEFAULT +
+                      ' environment variable)')
+        _raise_exception_for_reading_json(default_credential_filename,
+                                          extra_help, error)
+    elif well_known_file:
+      try:
+        return _get_default_credential_from_file(well_known_file)
+      except (DefaultCredentialsError, ValueError) as error:
+        extra_help = (' (produced automatically when running'
+                      ' "gcloud auth login" command)')
+        _raise_exception_for_reading_json(well_known_file, extra_help, error)
+    elif _env_name in ('GAE_PRODUCTION', 'GAE_LOCAL'):
+      return _get_default_credential_GAE()
+    elif _env_name == 'GCE_PRODUCTION':
+      return _get_default_credential_GCE()
+    else:
+      raise DefaultCredentialsError(
+          "The Default Credentials are not available. They are available if "
+          "running in Google App Engine or Google Compute Engine. They are "
+          "also available if using the Google Cloud SDK and running 'gcloud "
+          "auth login'. Otherwise, the environment variable " +
+          GOOGLE_CREDENTIALS_DEFAULT + " must be defined pointing to a file "
+          "defining the credentials. "
+          "See https://developers.google.com/accounts/docs/default-credentials "
+          "for details.")
+
+  @staticmethod
+  def from_stream(credential_filename):
+    """Create a Credentials object by reading the information from a given file.
+    
+    It returns an object of type GoogleCredentials.
+    
+    Args:
+      credential_filename: the path to the file from where the credentials
+        are to be read
+
+    Exceptions:
+      DefaultCredentialsError: raised when the credentials fail to be retrieved.
+    """
+
+    if credential_filename and os.path.isfile(credential_filename):
+      try:
+        return _get_default_credential_from_file(credential_filename)
+      except (DefaultCredentialsError, ValueError) as error:
+        extra_help = ' (provided as parameter to the from_stream() method)'
+        _raise_exception_for_reading_json(credential_filename,
+                                          extra_help,
+                                          error)
+    else:
+      raise DefaultCredentialsError('The parameter passed to the from_stream()'
+                                    ' method should point to a file.')
+
+
+def _get_environment_variable_file():
+  default_credential_filename = os.environ.get(GOOGLE_CREDENTIALS_DEFAULT,
+                                               None)
+
+  if default_credential_filename:
+    if os.path.isfile(default_credential_filename):
+      return default_credential_filename
+    else:
+      raise DefaultCredentialsError(
+          'File ' + default_credential_filename + ' (pointed by ' +
+          GOOGLE_CREDENTIALS_DEFAULT + ' environment variable) does not exist!')
+
+
+def _get_well_known_file():
+  """Get the well known file produced by command 'gcloud auth login'."""
+  # TODO(orestica): Revisit this method once gcloud provides a better way
+  # of pinpointing the exact location of the file.
+
+  WELL_KNOWN_CREDENTIALS_FILE = 'credentials_default.json'
+  CLOUDSDK_CONFIG_DIRECTORY = 'gcloud'
+
+  if os.name == 'nt':
+    try:
+      default_config_path = os.path.join(os.environ['APPDATA'],
+                                         CLOUDSDK_CONFIG_DIRECTORY)
+    except KeyError:
+      # This should never happen unless someone is really messing with things.
+      drive = os.environ.get('SystemDrive', 'C:')
+      default_config_path = os.path.join(drive, '\\', CLOUDSDK_CONFIG_DIRECTORY)
+  else:
+    default_config_path = os.path.join(os.path.expanduser('~'),
+                                       '.config',
+                                       CLOUDSDK_CONFIG_DIRECTORY)
+
+  default_config_path = os.path.join(default_config_path,
+                                     WELL_KNOWN_CREDENTIALS_FILE)
+
+  if os.path.isfile(default_config_path):
+    return default_config_path
+
+
+def _get_default_credential_from_file(default_credential_filename):
+  """Build the Default Credentials from file."""
+
+  import service_account
+
+  # read the credentials from the file
+  with open(default_credential_filename) as default_credential:
+    client_credentials = service_account.simplejson.load(default_credential)
+
+  credentials_type = client_credentials.get('type')
+  if credentials_type == AUTHORIZED_USER:
+    required_fields = set(['client_id', 'client_secret', 'refresh_token'])
+  elif credentials_type == SERVICE_ACCOUNT:
+    required_fields = set(['client_id', 'client_email', 'private_key_id',
+                           'private_key'])
+  else:
+    raise DefaultCredentialsError("'type' field should be defined "
+                                  "(and have one of the '" + AUTHORIZED_USER +
+                                  "' or '" + SERVICE_ACCOUNT + "' values)")
+
+  missing_fields = required_fields.difference(client_credentials.keys())
+  
+  if missing_fields:
+    _raise_exception_for_missing_fields(missing_fields)
+
+  if client_credentials['type'] == AUTHORIZED_USER:
+    return GoogleCredentials(
+        access_token=None,
+        client_id=client_credentials['client_id'],
+        client_secret=client_credentials['client_secret'],
+        refresh_token=client_credentials['refresh_token'],
+        token_expiry=None,
+        token_uri=GOOGLE_TOKEN_URI,
+        user_agent='Python client library')
+  else:  # client_credentials['type'] == SERVICE_ACCOUNT
+    return service_account._ServiceAccountCredentials(
+        service_account_id=client_credentials['client_id'],
+        service_account_email=client_credentials['client_email'],
+        private_key_id=client_credentials['private_key_id'],
+        private_key_pkcs8_text=client_credentials['private_key'],
+        scopes=[])
+
+
+def _raise_exception_for_missing_fields(missing_fields):
+  raise DefaultCredentialsError('The following field(s): ' +
+                                ', '.join(missing_fields) + ' must be defined.')
+
+
+def _raise_exception_for_reading_json(credential_file,
+                                      extra_help,
+                                      error):
+  raise DefaultCredentialsError('An error was encountered while reading '
+                                'json file: '+ credential_file + extra_help +
+                                ': ' + str(error))
+
+
+def _get_default_credential_GAE():
+  from oauth2client.appengine import AppAssertionCredentials
+
+  return AppAssertionCredentials([])
+
+
+def _get_default_credential_GCE():
+  from oauth2client.gce import AppAssertionCredentials
+
+  return AppAssertionCredentials([])
+
+
+class AssertionCredentials(GoogleCredentials):
   """Abstract Credentials object used for OAuth 2.0 assertion grants.
 
   This credential does not require a flow to instantiate because it
@@ -899,7 +1221,7 @@ if HAS_CRYPTO:
     later. For App Engine you may also consider using AppAssertionCredentials.
     """
 
-    MAX_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
+    MAX_TOKEN_LIFETIME_SECS = 3600  # 1 hour in seconds
 
     @util.positional(4)
     def __init__(self,
diff --git a/oauth2client/gce.py b/oauth2client/gce.py
index c7fd7c1..c9ff8f4 100644
--- a/oauth2client/gce.py
+++ b/oauth2client/gce.py
@@ -57,6 +57,7 @@ class AppAssertionCredentials(AssertionCredentials):
         requested.
     """
     self.scope = util.scopes_to_string(scope)
+    self.kwargs = kwargs
 
     # Assertion type is no longer used, but still in the parent class signature.
     super(AppAssertionCredentials, self).__init__(None)
@@ -87,4 +88,14 @@ class AppAssertionCredentials(AssertionCredentials):
         raise AccessTokenRefreshError(str(e))
       self.access_token = d['accessToken']
     else:
+      if response.status == 404:
+        content = content + (' This can occur if a VM was created'
+            ' with no service account or scopes.')
       raise AccessTokenRefreshError(content)
+
+  def create_scoped_required(self):
+    return not self.scope
+
+  def create_scoped(self, scopes):
+    return AppAssertionCredentials(scopes,
+                                   **self.kwargs)
diff --git a/oauth2client/service_account.py b/oauth2client/service_account.py
new file mode 100644
index 0000000..de8c0a2
--- /dev/null
+++ b/oauth2client/service_account.py
@@ -0,0 +1,121 @@
+# Copyright (C) 2014 Google Inc.
+#
+# 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.
+
+"""A service account credentials class.
+
+This credentials class is implemented on top of rsa library.
+"""
+
+import base64
+import rsa
+import time
+import types
+
+from oauth2client import GOOGLE_REVOKE_URI
+from oauth2client import GOOGLE_TOKEN_URI
+from oauth2client import util
+from oauth2client.anyjson import simplejson
+from oauth2client.client import AssertionCredentials
+
+from pyasn1.codec.ber import decoder
+from pyasn1_modules.rfc5208 import PrivateKeyInfo
+
+
+class _ServiceAccountCredentials(AssertionCredentials):
+  """Class representing a service account (signed JWT) credential."""
+
+  MAX_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
+
+  def __init__(self, service_account_id, service_account_email, private_key_id,
+      private_key_pkcs8_text, scopes, user_agent=None,
+      token_uri=GOOGLE_TOKEN_URI, revoke_uri=GOOGLE_REVOKE_URI, **kwargs):
+
+    super(_ServiceAccountCredentials, self).__init__(
+        None, user_agent=user_agent, token_uri=token_uri, revoke_uri=revoke_uri)
+    
+    self._service_account_id = service_account_id
+    self._service_account_email = service_account_email
+    self._private_key_id = private_key_id
+    self._private_key = _get_private_key(private_key_pkcs8_text)
+    self._private_key_pkcs8_text = private_key_pkcs8_text
+    self._scopes = util.scopes_to_string(scopes)
+    self._user_agent = user_agent
+    self._token_uri = token_uri
+    self._revoke_uri = revoke_uri
+    self._kwargs = kwargs
+
+  def _generate_assertion(self):
+    """Generate the assertion that will be used in the request."""
+
+    header = {
+        'alg': 'RS256',
+        'typ': 'JWT',
+        'kid': self._private_key_id
+    }
+
+    now = long(time.time())
+    payload = {
+        'aud': self._token_uri,
+        'scope': self._scopes,
+        'iat': now,
+        'exp': now + _ServiceAccountCredentials.MAX_TOKEN_LIFETIME_SECS,
+        'iss': self._service_account_email
+    }
+    payload.update(self._kwargs)
+
+    assertion_input = '%s.%s' % (
+        _urlsafe_b64encode(header),
+        _urlsafe_b64encode(payload))
+
+    # Sign the assertion.
+    signature = base64.urlsafe_b64encode(rsa.pkcs1.sign(
+        assertion_input, self._private_key, 'SHA-256')).rstrip('=')
+
+    return '%s.%s' % (assertion_input, signature)
+
+  def sign_blob(self, blob):
+    return (self._private_key_id,
+            rsa.pkcs1.sign(blob, self._private_key, 'SHA-256'))
+
+  @property
+  def service_account_email(self):
+    return self._service_account_email
+
+  def create_scoped_required(self):
+    return not self._scopes
+
+  def create_scoped(self, scopes):
+    return _ServiceAccountCredentials(self._service_account_id,
+                                      self._service_account_email,
+                                      self._private_key_id,
+                                      self._private_key_pkcs8_text,
+                                      scopes,
+                                      user_agent=self._user_agent,
+                                      token_uri=self._token_uri,
+                                      revoke_uri=self._revoke_uri,
+                                      **self._kwargs)
+
+def _urlsafe_b64encode(data):
+  return base64.urlsafe_b64encode(
+      simplejson.dumps(data, separators = (',', ':'))\
+          .encode('UTF-8')).rstrip('=')
+
+def _get_private_key(private_key_pkcs8_text):
+  """Get an RSA private key object from a pkcs8 representation."""
+
+  der = rsa.pem.load_pem(private_key_pkcs8_text, 'PRIVATE KEY')
+  asn1_private_key, _ = decoder.decode(der, asn1Spec=PrivateKeyInfo())
+  return rsa.PrivateKey.load_pkcs1(
+      asn1_private_key.getComponentByName('privateKey').asOctets(),
+      format='DER')
diff --git a/samples/call_compute_service.py b/samples/call_compute_service.py
new file mode 100644
index 0000000..aaa4f38
--- /dev/null
+++ b/samples/call_compute_service.py
@@ -0,0 +1,15 @@
+# To be used to test GoogleCredential.GetDefaultCredential()
+# from local machine and GCE.
+
+from googleapiclient.discovery import build
+from oauth2client.client import GoogleCredentials
+
+PROJECT = "bamboo-machine-422"  # Provide your own GCE project here
+ZONE = "us-central1-a"          # Put here a zone which has some VMs
+
+service = build("compute", "v1", credentials=GoogleCredentials.get_default())
+
+request = service.instances().list(project=PROJECT, zone=ZONE)
+response = request.execute()
+
+print response
diff --git a/samples/googleappengine/app.yaml b/samples/googleappengine/app.yaml
new file mode 100644
index 0000000..a299030
--- /dev/null
+++ b/samples/googleappengine/app.yaml
@@ -0,0 +1,10 @@
+application: bamboo-machine-422
+version: 2
+runtime: python27
+api_version: 1
+threadsafe: true
+
+handlers:
+- url: /.*
+  script: call_compute_service_from_gae.app
+
diff --git a/samples/googleappengine/call_compute_service_from_gae.py b/samples/googleappengine/call_compute_service_from_gae.py
new file mode 100644
index 0000000..e2b01d2
--- /dev/null
+++ b/samples/googleappengine/call_compute_service_from_gae.py
@@ -0,0 +1,21 @@
+# To be used to test GoogleCredential.GetDefaultCredential()
+# from devel GAE (ie, dev_appserver.py).
+
+import webapp2
+from googleapiclient.discovery import build
+from oauth2client.client import GoogleCredentials
+
+PROJECT = "bamboo-machine-422"  # Provide your own GCE project here
+ZONE = "us-central1-a"          # Put here a zone which has some VMs
+
+def get_instances():
+  service = build("compute", "v1", credentials=GoogleCredentials.get_default())
+  request = service.instances().list(project=PROJECT, zone=ZONE)
+  return request.execute()
+
+class MainPage(webapp2.RequestHandler):
+
+  def get(self):
+    self.response.write(get_instances())
+
+app = webapp2.WSGIApplication([('/', MainPage),], debug=True)
diff --git a/setup.py b/setup.py
index 552a50d..4e738fa 100644
--- a/setup.py
+++ b/setup.py
@@ -26,6 +26,9 @@ packages = [
 
 install_requires = [
     'httplib2>=0.8',
+    'pyasn1==0.1.7',
+    'pyasn1_modules==0.0.5',
+    'rsa==3.1.4',
 ]
 
 needs_json = False
diff --git a/tests/data/gcloud/credentials_default.json b/tests/data/gcloud/credentials_default.json
new file mode 100644
index 0000000..1d4bad1
--- /dev/null
+++ b/tests/data/gcloud/credentials_default.json
@@ -0,0 +1,9 @@
+{
+  "type": "service_account",
+  "client_id": "123",
+  "client_secret": "secret",
+  "refresh_token": "alabalaportocala",
+  "client_email": "dummy@google.com",
+  "private_key_id": "ABCDEF",
+  "private_key": "Bag Attributes\n    friendlyName: key\n    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC\nKey Attributes: <No Attributes>\n-----BEGIN PRIVATE KEY-----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\nVL5h7N0VstYhGgycuPpcIUQa\n-----END PRIVATE KEY-----\n"
+}
\ No newline at end of file
diff --git a/tests/data/gcloud/credentials_default_authorized_user.json b/tests/data/gcloud/credentials_default_authorized_user.json
new file mode 100644
index 0000000..76addd5
--- /dev/null
+++ b/tests/data/gcloud/credentials_default_authorized_user.json
@@ -0,0 +1,9 @@
+{
+  "type": "authorized_user",
+  "client_id": "123",
+  "client_secret": "secret",
+  "refresh_token": "alabalaportocala",
+  "client_email": "dummy@google.com",
+  "private_key_id": "ABCDEF",
+  "private_key": "Bag Attributes\n    friendlyName: key\n    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC\nKey Attributes: <No Attributes>\n-----BEGIN PRIVATE KEY-----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\nVL5h7N0VstYhGgycuPpcIUQa\n-----END PRIVATE KEY-----\n"
+}
\ No newline at end of file
diff --git a/tests/data/gcloud/credentials_default_malformed_1.json b/tests/data/gcloud/credentials_default_malformed_1.json
new file mode 100644
index 0000000..fe9fd1e
--- /dev/null
+++ b/tests/data/gcloud/credentials_default_malformed_1.json
@@ -0,0 +1,9 @@
+{
+  "type": "serviceaccount",
+  "client_id": "123",
+  "client_secret": "secret",
+  "refresh_token": "alabalaportocala",
+  "client_email": "dummy@google.com",
+  "private_key_id": "ABCDEF",
+  "private_key": "Bag Attributes\n    friendlyName: key\n    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC\nKey Attributes: <No Attributes>\n-----BEGIN PRIVATE KEY-----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\nVL5h7N0VstYhGgycuPpcIUQa\n-----END PRIVATE KEY-----\n"
+}
\ No newline at end of file
diff --git a/tests/data/gcloud/credentials_default_malformed_2.json b/tests/data/gcloud/credentials_default_malformed_2.json
new file mode 100644
index 0000000..6f1ae52
--- /dev/null
+++ b/tests/data/gcloud/credentials_default_malformed_2.json
@@ -0,0 +1,8 @@
+{
+  "type": "service_account",
+  "client_id": "123",
+  "client_secret": "secret",
+  "refresh_token": "alabalaportocala",
+  "client_email": "dummy@google.com",
+  "private_key": "Bag Attributes\n    friendlyName: key\n    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC\nKey Attributes: <No Attributes>\n-----BEGIN PRIVATE KEY-----\nMIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDh6PSnttDsv+vi\ntUZTP1E3hVBah6PUGDWZhYgNiyW8quTWCmPvBmCR2YzuhUrY5+CtKP8UJOQico+p\noJHSAPsrzSr6YsGs3c9SQOslBmm9Fkh9/f/GZVTVZ6u5AsUmOcVvZ2q7Sz8Vj/aR\naIm0EJqRe9cQ5vvN9sg25rIv4xKwIZJ1VixKWJLmpCmDINqn7xvl+ldlUmSr3aGt\nw21uSDuEJhQlzO3yf2FwJMkJ9SkCm9oVDXyl77OnKXj5bOQ/rojbyGeIxDJSUDWE\nGKyRPuqKi6rSbwg6h2G/Z9qBJkqM5NNTbGRIFz/9/LdmmwvtaqCxlLtD7RVEryAp\n+qTGDk5hAgMBAAECggEBAMYYfNDEYpf4A2SdCLne/9zrrfZ0kphdUkL48MDPj5vN\nTzTRj6f9s5ixZ/+QKn3hdwbguCx13QbH5mocP0IjUhyqoFFHYAWxyyaZfpjM8tO4\nQoEYxby3BpjLe62UXESUzChQSytJZFwIDXKcdIPNO3zvVzufEJcfG5no2b9cIvsG\nDy6J1FNILWxCtDIqBM+G1B1is9DhZnUDgn0iKzINiZmh1I1l7k/4tMnozVIKAfwo\nf1kYjG/d2IzDM02mTeTElz3IKeNriaOIYTZgI26xLJxTkiFnBV4JOWFAZw15X+yR\n+DrjGSIkTfhzbLa20Vt3AFM+LFK0ZoXT2dRnjbYPjQECgYEA+9XJFGwLcEX6pl1p\nIwXAjXKJdju9DDn4lmHTW0Pbw25h1EXONwm/NPafwsWmPll9kW9IwsxUQVUyBC9a\nc3Q7rF1e8ai/qqVFRIZof275MI82ciV2Mw8Hz7FPAUyoju5CvnjAEH4+irt1VE/7\nSgdvQ1gDBQFegS69ijdz+cOhFxkCgYEA5aVoseMy/gIlsCvNPyw9+Jz/zBpKItX0\njGzdF7lhERRO2cursujKaoHntRckHcE3P/Z4K565bvVq+VaVG0T/BcBKPmPHrLmY\niuVXidltW7Jh9/RCVwb5+BvqlwlC470PEwhqoUatY/fPJ74srztrqJHvp1L29FT5\nsdmlJW8YwokCgYAUa3dMgp5C0knKp5RY1KSSU5E11w4zKZgwiWob4lq1dAPWtHpO\nGCo63yyBHImoUJVP75gUw4Cpc4EEudo5tlkIVuHV8nroGVKOhd9/Rb5K47Hke4kk\nBrn5a0Ues9qPDF65Fw1ryPDFSwHufjXAAO5SpZZJF51UGDgiNvDedbBgMQKBgHSk\nt7DjPhtW69234eCckD2fQS5ijBV1p2lMQmCygGM0dXiawvN02puOsCqDPoz+fxm2\nDwPY80cw0M0k9UeMnBxHt25JMDrDan/iTbxu++T/jlNrdebOXFlxlI5y3c7fULDS\nLZcNVzTXwhjlt7yp6d0NgzTyJw2ju9BiREfnTiRBAoGBAOPHrTOnPyjO+bVcCPTB\nWGLsbBd77mVPGIuL0XGrvbVYPE8yIcNbZcthd8VXL/38Ygy8SIZh2ZqsrU1b5WFa\nXUMLnGEODSS8x/GmW3i3KeirW5OxBNjfUzEF4XkJP8m41iTdsQEXQf9DdUY7X+CB\nVL5h7N0VstYhGgycuPpcIUQa\n-----END PRIVATE KEY-----\n"
+}
\ No newline at end of file
diff --git a/tests/data/gcloud/credentials_default_malformed_3.json b/tests/data/gcloud/credentials_default_malformed_3.json
new file mode 100644
index 0000000..efed137
--- /dev/null
+++ b/tests/data/gcloud/credentials_default_malformed_3.json
@@ -0,0 +1,9 @@
+{
+  "type": "service_account"
+  "client_id": "123",
+  "client_secret": "secret",
+  "refresh_token": "alabalaportocala",
+  "client_email": "dummy@google.com",
+  "private_key_id": "ABCDEF",
+  "private_key": "Bag Attributes\n    friendlyName: key\n    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC\nKey Attributes: <No Attributes>\n-----BEGIN PRIVATE KEY-----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\nVL5h7N0VstYhGgycuPpcIUQa\n-----END PRIVATE KEY-----\n"
+}
\ No newline at end of file
diff --git a/tests/data/publickey_openssl.pem b/tests/data/publickey_openssl.pem
new file mode 100644
index 0000000..893ee79
--- /dev/null
+++ b/tests/data/publickey_openssl.pem
@@ -0,0 +1,9 @@
+-----BEGIN PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4ej0p7bQ7L/r4rVGUz9R
+N4VQWoej1Bg1mYWIDYslvKrk1gpj7wZgkdmM7oVK2OfgrSj/FCTkInKPqaCR0gD7
+K80q+mLBrN3PUkDrJQZpvRZIff3/xmVU1WeruQLFJjnFb2dqu0s/FY/2kWiJtBCa
+kXvXEOb7zfbINuayL+MSsCGSdVYsSliS5qQpgyDap+8b5fpXZVJkq92hrcNtbkg7
+hCYUJczt8n9hcCTJCfUpApvaFQ18pe+zpyl4+WzkP66I28hniMQyUlA1hBiskT7q
+iouq0m8IOodhv2fagSZKjOTTU2xkSBc//fy3ZpsL7WqgsZS7Q+0VRK8gKfqkxg5O
+YQIDAQAB
+-----END PUBLIC KEY-----
diff --git a/tests/test_appengine.py b/tests/test_appengine.py
index 8a3a9ee..e75ca88 100644
--- a/tests/test_appengine.py
+++ b/tests/test_appengine.py
@@ -220,6 +220,33 @@ class TestAppAssertionCredentials(unittest.TestCase):
     self.assertEqual('a_token_456', credentials.access_token)
     self.assertEqual(scope, credentials.scope)
 
+  def test_create_scoped_required_without_scopes(self):
+    credentials = AppAssertionCredentials([])
+    self.assertTrue(credentials.create_scoped_required())
+
+  def test_create_scoped_required_with_scopes(self):
+    credentials = AppAssertionCredentials(['dummy_scope'])
+    self.assertFalse(credentials.create_scoped_required())
+
+  def test_create_scoped(self):
+    credentials = AppAssertionCredentials([])
+    new_credentials = credentials.create_scoped(['dummy_scope'])
+    self.assertNotEqual(credentials, new_credentials)
+    self.assertTrue(isinstance(new_credentials, AppAssertionCredentials))
+    self.assertEqual('dummy_scope', new_credentials.scope)
+
+  def test_get_access_token(self):
+    app_identity_stub = self.AppIdentityStubImpl()
+    apiproxy_stub_map.apiproxy = apiproxy_stub_map.APIProxyStubMap()
+    apiproxy_stub_map.apiproxy.RegisterStub("app_identity_service",
+                                            app_identity_stub)
+    apiproxy_stub_map.apiproxy.RegisterStub(
+        'memcache', memcache_stub.MemcacheServiceStub())
+
+    credentials = AppAssertionCredentials(['dummy_scope'])
+    token = credentials.get_access_token()
+    self.assertEqual('a_token_123', token)
+
 
 class TestFlowModel(db.Model):
   flow = FlowProperty()
diff --git a/tests/test_gce.py b/tests/test_gce.py
index 15e45c4..ec87512 100644
--- a/tests/test_gce.py
+++ b/tests/test_gce.py
@@ -20,8 +20,9 @@ Unit tests for oauth2client.gce.
 
 __author__ = 'jcgregorio@google.com (Joe Gregorio)'
 
-import unittest
+import httplib2
 import mox
+import unittest
 
 from oauth2client.client import AccessTokenRefreshError
 from oauth2client.client import Credentials
@@ -55,7 +56,6 @@ class AssertionCredentialsTests(unittest.TestCase):
     m.UnsetStubs()
     m.VerifyAll()
 
-
   def test_fail_refresh(self):
     m = mox.Mox()
 
@@ -90,3 +90,44 @@ class AssertionCredentialsTests(unittest.TestCase):
     c2 = Credentials.new_from_json(json)
 
     self.assertEqual(c.access_token, c2.access_token)
+
+  def test_create_scoped_required_without_scopes(self):
+    credentials = AppAssertionCredentials([])
+    self.assertTrue(credentials.create_scoped_required())
+
+  def test_create_scoped_required_with_scopes(self):
+    credentials = AppAssertionCredentials(['dummy_scope'])
+    self.assertFalse(credentials.create_scoped_required())
+
+  def test_create_scoped(self):
+    credentials = AppAssertionCredentials([])
+    new_credentials = credentials.create_scoped(['dummy_scope'])
+    self.assertNotEqual(credentials, new_credentials)
+    self.assertTrue(isinstance(new_credentials, AppAssertionCredentials))
+    self.assertEqual('dummy_scope', new_credentials.scope)
+
+  def test_get_access_token(self):
+    m = mox.Mox()
+
+    httplib2_response = m.CreateMock(object)
+    httplib2_response.status = 200
+
+    httplib2_request = m.CreateMock(object)
+    httplib2_request.__call__(
+        ('http://metadata.google.internal/0.1/meta-data/service-accounts/'
+         'default/acquire?scope=dummy_scope'
+        )).AndReturn((httplib2_response, '{"accessToken": "this-is-a-token"}'))
+
+    m.ReplayAll()
+
+    credentials = AppAssertionCredentials(['dummy_scope'])
+
+    http = httplib2.Http()
+    http.request = httplib2_request
+
+    self.assertEquals('this-is-a-token',
+                      credentials.get_access_token(http=http))
+
+    m.UnsetStubs()
+    m.VerifyAll()
+    
diff --git a/tests/test_oauth2client.py b/tests/test_oauth2client.py
index ab44e2a..4d9771d 100644
--- a/tests/test_oauth2client.py
+++ b/tests/test_oauth2client.py
@@ -24,7 +24,9 @@ __author__ = 'jcgregorio@google.com (Joe Gregorio)'
 
 import base64
 import datetime
+import mox
 import os
+import time
 import unittest
 import urlparse
 
@@ -37,23 +39,36 @@ from oauth2client.client import AccessTokenCredentials
 from oauth2client.client import AccessTokenCredentialsError
 from oauth2client.client import AccessTokenRefreshError
 from oauth2client.client import AssertionCredentials
+from oauth2client.client import AUTHORIZED_USER
 from oauth2client.client import Credentials
+from oauth2client.client import DefaultCredentialsError
 from oauth2client.client import FlowExchangeError
+from oauth2client.client import GoogleCredentials
+from oauth2client.client import GOOGLE_CREDENTIALS_DEFAULT
 from oauth2client.client import MemoryCache
 from oauth2client.client import NonAsciiHeaderError
 from oauth2client.client import OAuth2Credentials
 from oauth2client.client import OAuth2WebServerFlow
 from oauth2client.client import OOB_CALLBACK_URN
 from oauth2client.client import REFRESH_STATUS_CODES
+from oauth2client.client import SERVICE_ACCOUNT
 from oauth2client.client import Storage
 from oauth2client.client import TokenRevokeError
 from oauth2client.client import VerifyJwtTokenError
+from oauth2client.client import _env_name
 from oauth2client.client import _extract_id_token
+from oauth2client.client import _get_default_credential_from_file
+from oauth2client.client import _get_environment
+from oauth2client.client import _get_environment_variable_file
+from oauth2client.client import _get_well_known_file
+from oauth2client.client import _raise_exception_for_missing_fields
+from oauth2client.client import _raise_exception_for_reading_json
 from oauth2client.client import _update_query_params
 from oauth2client.client import credentials_from_clientsecrets_and_code
 from oauth2client.client import credentials_from_code
 from oauth2client.client import flow_from_clientsecrets
 from oauth2client.clientsecrets import _loadfile
+from oauth2client.service_account import _ServiceAccountCredentials
 
 DATA_DIR = os.path.join(os.path.dirname(__file__), 'data')
 
@@ -107,6 +122,328 @@ class CredentialsTests(unittest.TestCase):
     restored = Credentials.new_from_json(json)
 
 
+class MockResponse(object):
+  """Mock the response of urllib2.urlopen() call."""
+  
+  def __init__(self, headers):
+    self._headers = headers
+
+  def info(self):
+    class Info:
+      def __init__(self, headers):
+        self.headers = headers
+
+    return Info(self._headers)
+
+
+class GoogleCredentialsTests(unittest.TestCase):
+
+  def setUp(self):
+    self.env_server_software = os.environ.get('SERVER_SOFTWARE', None)
+    self.env_google_credentials_default = (
+        os.environ.get(GOOGLE_CREDENTIALS_DEFAULT, None))
+    self.env_appdata = os.environ.get('APPDATA', None)
+    self.os_name = os.name
+    from oauth2client import client
+    setattr(client, '_env_name', None)
+
+  def tearDown(self):
+    self.reset_env('SERVER_SOFTWARE', self.env_server_software)
+    self.reset_env(GOOGLE_CREDENTIALS_DEFAULT,
+                   self.env_google_credentials_default)
+    self.reset_env('APPDATA', self.env_appdata)
+    os.name = self.os_name
+
+  def reset_env(self, env, value):
+    """Set the environment variable 'env' to 'value'."""
+    if value is not None:
+      os.environ[env] = value
+    else:
+      os.environ.pop(env, '')
+
+  def validate_service_account_credentials(self, credentials):
+    self.assertTrue(isinstance(credentials, _ServiceAccountCredentials))
+    self.assertEqual('123', credentials._service_account_id)
+    self.assertEqual('dummy@google.com', credentials._service_account_email)
+    self.assertEqual('ABCDEF', credentials._private_key_id)
+    self.assertEqual('', credentials._scopes)
+
+  def validate_google_credentials(self, credentials):
+    self.assertTrue(isinstance(credentials, GoogleCredentials))
+    self.assertEqual(None, credentials.access_token)
+    self.assertEqual('123', credentials.client_id)
+    self.assertEqual('secret', credentials.client_secret)
+    self.assertEqual('alabalaportocala', credentials.refresh_token)
+    self.assertEqual(None, credentials.token_expiry)
+    self.assertEqual(GOOGLE_TOKEN_URI, credentials.token_uri)
+    self.assertEqual('Python client library', credentials.user_agent)
+
+  def get_a_google_credentials_object(self):
+    return GoogleCredentials(None, None, None, None, None, None, None, None)
+
+  def test_create_scoped_required(self):
+    self.assertFalse(
+        self.get_a_google_credentials_object().create_scoped_required())
+
+  def test_create_scoped(self):
+    credentials = self.get_a_google_credentials_object() 
+    self.assertEqual(credentials, credentials.create_scoped(None))
+    self.assertEqual(credentials,
+                     credentials.create_scoped(['dummy_scope']))
+
+  def test_get_environment_gae_production(self):
+    os.environ['SERVER_SOFTWARE'] = 'Google App Engine/XYZ'
+    self.assertEqual('GAE_PRODUCTION', _get_environment())
+
+  def test_get_environment_gae_local(self):
+    os.environ['SERVER_SOFTWARE'] = 'Development/XYZ'
+    self.assertEqual('GAE_LOCAL', _get_environment())
+
+  def test_get_environment_gce_production(self):
+    os.environ['SERVER_SOFTWARE'] = ''
+    mockResponse = MockResponse(['Metadata-Flavor: Google\r\n'])
+
+    m = mox.Mox()
+
+    urllib2_urlopen = m.CreateMock(object)
+    urllib2_urlopen.__call__(('http://metadata.google.internal'
+                             )).AndReturn(mockResponse)
+
+    m.ReplayAll()
+
+    self.assertEqual('GCE_PRODUCTION', _get_environment(urllib2_urlopen))
+
+    m.UnsetStubs()
+    m.VerifyAll()
+
+  def test_get_environment_unknown(self):
+    os.environ['SERVER_SOFTWARE'] = ''
+    mockResponse = MockResponse([])
+
+    m = mox.Mox()
+
+    urllib2_urlopen = m.CreateMock(object)
+    urllib2_urlopen.__call__(('http://metadata.google.internal'
+                             )).AndReturn(mockResponse)
+
+    m.ReplayAll()
+
+    self.assertEqual('UNKNOWN', _get_environment(urllib2_urlopen))
+
+    m.UnsetStubs()
+    m.VerifyAll()
+
+  def test_get_environment_variable_file(self):
+    environment_variable_file = datafile(
+        os.path.join('gcloud', 'credentials_default.json'))
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = environment_variable_file
+    self.assertEqual(environment_variable_file,
+                     _get_environment_variable_file())
+
+  def test_get_environment_variable_file_error(self):
+    nonexistent_file = datafile('nonexistent')
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = nonexistent_file
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      _get_environment_variable_file()
+      self.fail(nonexistent_file + ' should not exist.')
+    except DefaultCredentialsError as error:
+      self.assertEqual('File ' + nonexistent_file +
+                       ' (pointed by ' + GOOGLE_CREDENTIALS_DEFAULT +
+                       ' environment variable) does not exist!',
+                       str(error))
+
+  def test_get_well_known_file_on_windows(self):
+    well_known_file = datafile(
+        os.path.join('gcloud', 'credentials_default.json'))
+    os.name = 'nt'
+    os.environ['APPDATA'] = DATA_DIR
+    self.assertEqual(well_known_file, _get_well_known_file())
+
+  def test_get_well_known_file_on_windows_no_file(self):
+    os.name = 'nt'
+    os.environ['APPDATA'] = os.path.join(DATA_DIR, 'nonexistentpath')
+    self.assertEqual(None, _get_well_known_file())
+
+  def test_get_default_credential_from_file_service_account(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default.json'))
+    credentials = _get_default_credential_from_file(credentials_file)
+    self.validate_service_account_credentials(credentials)
+
+  def test_get_default_credential_from_file_authorized_user(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_authorized_user.json'))
+    credentials = _get_default_credential_from_file(credentials_file)
+    self.validate_google_credentials(credentials)
+
+  def test_get_default_credential_from_malformed_file_1(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_1.json'))
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      _get_default_credential_from_file(credentials_file)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual("'type' field should be defined "
+                       "(and have one of the '" + AUTHORIZED_USER +
+                       "' or '" + SERVICE_ACCOUNT + "' values)",
+                       str(error))
+
+  def test_get_default_credential_from_malformed_file_2(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_2.json'))
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      _get_default_credential_from_file(credentials_file)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual('The following field(s): '
+                       'private_key_id must be defined.',
+                       str(error))
+
+  def test_get_default_credential_from_malformed_file_3(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_3.json'))
+    self.assertRaises(ValueError, _get_default_credential_from_file,
+                      credentials_file)
+
+  def test_raise_exception_for_missing_fields(self):
+    missing_fields = ['first', 'second', 'third']
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      _raise_exception_for_missing_fields(missing_fields)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual('The following field(s): ' +
+                       ', '.join(missing_fields) + ' must be defined.',
+                       str(error))
+
+  def test_raise_exception_for_reading_json(self):
+    credential_file = 'any_file'
+    extra_help = ' be good'
+    error = DefaultCredentialsError('stuff happens')
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      _raise_exception_for_reading_json(credential_file, extra_help, error)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as ex:
+      self.assertEqual('An error was encountered while reading '
+                       'json file: '+ credential_file +
+                       extra_help + ': ' + str(error),
+                       str(ex))
+
+  def test_get_default_from_environment_variable_service_account(self):
+    os.environ['SERVER_SOFTWARE'] = ''
+    environment_variable_file = datafile(
+        os.path.join('gcloud', 'credentials_default.json'))
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = environment_variable_file
+    self.validate_service_account_credentials(GoogleCredentials.get_default())
+
+  def test_env_name(self):
+    from oauth2client import client
+    self.assertEqual(None, getattr(client, '_env_name'))
+    self.test_get_default_from_environment_variable_service_account()
+    self.assertEqual('UNKNOWN', getattr(client, '_env_name'))    
+
+  def test_get_default_from_environment_variable_authorized_user(self):
+    os.environ['SERVER_SOFTWARE'] = ''
+    environment_variable_file = datafile(
+        os.path.join('gcloud', 'credentials_default_authorized_user.json'))
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = environment_variable_file
+    self.validate_google_credentials(GoogleCredentials.get_default())
+
+  def test_get_default_from_environment_variable_malformed_file(self):
+    os.environ['SERVER_SOFTWARE'] = ''
+    environment_variable_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_3.json'))
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = environment_variable_file
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      GoogleCredentials.get_default()
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertTrue(str(error).startswith(
+          'An error was encountered while reading json file: ' +
+          environment_variable_file + ' (pointed to by ' +
+          GOOGLE_CREDENTIALS_DEFAULT + ' environment variable):'))
+
+  def test_get_default_environment_not_set_up(self):
+    # It is normal for this test to fail if run inside
+    # a Google Compute Engine VM or after 'gcloud auth login' command
+    # has been executed on a non Windows machine.
+    os.environ['SERVER_SOFTWARE'] = ''
+    os.environ[GOOGLE_CREDENTIALS_DEFAULT] = ''
+    os.environ['APPDATA'] = ''
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      GoogleCredentials.get_default()
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual("The Default Credentials are not available. They are "
+                       "available if running in Google App Engine or Google "
+                       "Compute Engine. They are also available if using the "
+                       "Google Cloud SDK and running 'gcloud auth login'. "
+                       "Otherwise, the environment variable " +
+                       GOOGLE_CREDENTIALS_DEFAULT + " must be defined pointing "
+                       "to a file defining the credentials. See "
+                       "https://developers.google.com/accounts/docs/default-"
+                       "credentials for details.",
+                        str(error))
+
+  def test_from_stream_service_account(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default.json'))
+    credentials = (
+        self.get_a_google_credentials_object().from_stream(credentials_file))
+    self.validate_service_account_credentials(credentials)
+
+  def test_from_stream_authorized_user(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_authorized_user.json'))
+    credentials = (
+        self.get_a_google_credentials_object().from_stream(credentials_file))
+    self.validate_google_credentials(credentials)
+
+  def test_from_stream_malformed_file_1(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_1.json'))
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      self.get_a_google_credentials_object().from_stream(credentials_file)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual("An error was encountered while reading json file: " +
+                       credentials_file +
+                       " (provided as parameter to the from_stream() method): "
+                       "'type' field should be defined (and have one of the '" +
+                       AUTHORIZED_USER + "' or '" + SERVICE_ACCOUNT +
+                       "' values)",
+                       str(error))
+
+  def test_from_stream_malformed_file_2(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_2.json'))
+    # we can't use self.assertRaisesRegexp() because it is only in Python 2.7+
+    try:
+      self.get_a_google_credentials_object().from_stream(credentials_file)
+      self.fail('An exception was expected!')
+    except DefaultCredentialsError as error:
+      self.assertEqual('An error was encountered while reading json file: ' +
+                       credentials_file +
+                       ' (provided as parameter to the from_stream() method): '
+                       'The following field(s): private_key_id must be '
+                       'defined.',
+                       str(error))
+
+  def test_from_stream_malformed_file_3(self):
+    credentials_file = datafile(
+        os.path.join('gcloud', 'credentials_default_malformed_3.json'))
+    self.assertRaises(
+        DefaultCredentialsError,
+        self.get_a_google_credentials_object().from_stream, credentials_file)
+
+
 class DummyDeleteStorage(Storage):
   delete_called = False
 
@@ -245,6 +582,32 @@ class BasicCredentialsTests(unittest.TestCase):
     instance = OAuth2Credentials.from_json(self.credentials.to_json())
     self.assertEqual('foobar', instance.token_response)
 
+  def test_get_access_token(self):
+    token_response_first = {'access_token': 'first_token', 'expires_in': 1}
+    token_response_second = {'access_token': 'second_token', 'expires_in': 1}
+    http = HttpMockSequence([
+        ({'status': '200'}, simplejson.dumps(token_response_first)),
+        ({'status': '200'}, simplejson.dumps(token_response_second)),
+    ])
+
+    self.assertEqual('first_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_first, self.credentials.token_response)
+
+    self.assertEqual('first_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_first, self.credentials.token_response)
+
+    time.sleep(1)
+    self.assertTrue(self.credentials.access_token_expired)
+
+    self.assertEqual('second_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_second, self.credentials.token_response)
+
 
 class AccessTokenCredentialsTests(unittest.TestCase):
 
diff --git a/tests/test_service_account.py b/tests/test_service_account.py
new file mode 100644
index 0000000..f31394f
--- /dev/null
+++ b/tests/test_service_account.py
@@ -0,0 +1,120 @@
+#!/usr/bin/python2.4
+#
+# Copyright 2014 Google Inc.
+#
+# 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.
+
+
+"""Oauth2client tests.
+
+Unit tests for service account credentials implemented using RSA.
+"""
+
+import os
+import rsa
+import time
+import unittest
+
+from http_mock import HttpMockSequence
+from oauth2client.anyjson import simplejson
+from oauth2client.service_account import _ServiceAccountCredentials
+
+
+def datafile(filename):
+  # TODO(orestica): Refactor this using pkgutil.get_data
+  f = open(os.path.join(os.path.dirname(__file__), 'data', filename), 'r')
+  data = f.read()
+  f.close()
+  return data
+
+
+class ServiceAccountCredentialsTests(unittest.TestCase):
+  def setUp(self):
+    self.service_account_id = '123'
+    self.service_account_email = 'dummy@google.com'
+    self.private_key_id = 'ABCDEF'
+    self.private_key = datafile('pem_from_pkcs12.pem')
+    self.scopes = ['dummy_scope']
+    self.credentials = _ServiceAccountCredentials(self.service_account_id,
+                                                  self.service_account_email,
+                                                  self.private_key_id,
+                                                  self.private_key,
+                                                  [])
+
+  def test_sign_blob(self):
+    private_key_id, signature = self.credentials.sign_blob('Google')
+    self.assertEqual( self.private_key_id, private_key_id)
+
+    pub_key = rsa.PublicKey.load_pkcs1_openssl_pem(
+        datafile('publickey_openssl.pem'))
+
+    self.assertTrue(rsa.pkcs1.verify('Google', signature, pub_key))
+
+    try:
+      rsa.pkcs1.verify('Orest', signature, pub_key)
+      self.fail('Verification should have failed!')
+    except rsa.pkcs1.VerificationError:
+      pass  # Expected
+
+    try:
+      rsa.pkcs1.verify('Google', 'bad signature', pub_key)
+      self.fail('Verification should have failed!')
+    except rsa.pkcs1.VerificationError:
+      pass  # Expected
+
+  def test_service_account_email(self):
+    self.assertEqual(self.service_account_email,
+                     self.credentials.service_account_email)
+
+  def test_create_scoped_required_without_scopes(self):
+    self.assertTrue(self.credentials.create_scoped_required())
+
+  def test_create_scoped_required_with_scopes(self):
+    self.credentials = _ServiceAccountCredentials(self.service_account_id,
+                                                  self.service_account_email,
+                                                  self.private_key_id,
+                                                  self.private_key,
+                                                  self.scopes)
+    self.assertFalse(self.credentials.create_scoped_required())
+
+  def test_create_scoped(self):
+    new_credentials = self.credentials.create_scoped(self.scopes)
+    self.assertNotEqual(self.credentials, new_credentials)
+    self.assertTrue(isinstance(new_credentials, _ServiceAccountCredentials))
+    self.assertEqual('dummy_scope', new_credentials._scopes)
+
+  def test_access_token(self):
+    token_response_first = {'access_token': 'first_token', 'expires_in': 1}
+    token_response_second = {'access_token': 'second_token', 'expires_in': 1}
+    http = HttpMockSequence([
+        ({'status': '200'}, simplejson.dumps(token_response_first)),
+        ({'status': '200'}, simplejson.dumps(token_response_second)),
+    ])
+  
+    self.assertEqual('first_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_first, self.credentials.token_response)
+
+    self.assertEqual('first_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_first, self.credentials.token_response)
+
+    time.sleep(1)
+    self.assertTrue(self.credentials.access_token_expired)
+
+    self.assertEqual('second_token',
+                     self.credentials.get_access_token(http=http))
+    self.assertFalse(self.credentials.access_token_expired)
+    self.assertEqual(token_response_second, self.credentials.token_response)