Simplified OAuth2 flow (#762)

* Add `gspread.auth` module. 
`gspread.auth.oauth()` uses `InstalledAppFlow` from `google_auth_oauthlib` to implement OAuth 2.0 Authorization flow for installed applications.

* Handle configuration dir path for Windows as well

* Update test requirements

gspread/__init__.py

@@ -13,6 +13,7 @@
 __author__ = 'Anton Burnashev'
 
 
+from .auth import oauth
 from .client import Client
 from .models import Spreadsheet, Worksheet, Cell
 

gspread/auth.py

@@ -0,0 +1,102 @@
+# -*- coding: utf-8 -*-
+
+"""
+gspread.auth
+~~~~~~~~~~~~
+
+Simple authentication with OAuth.
+
+"""
+
+import os
+from google.oauth2.credentials import Credentials
+from google_auth_oauthlib.flow import InstalledAppFlow
+
+from .client import Client
+
+DEFAULT_SCOPES = [
+    'https://www.googleapis.com/auth/spreadsheets',
+    'https://www.googleapis.com/auth/drive'
+]
+
+READONLY_SCOPES = [
+    'https://www.googleapis.com/auth/spreadsheets.readonly',
+    'https://www.googleapis.com/auth/drive.readonly'
+]
+
+
+def get_config_dir(config_dir_name='gspread', os_is_windows=os.name == 'nt'):
+    """Construct a config dir path.
+
+    By default:
+        * `%APPDATA%\gspread` on Windows
+        * `~/.config/gspread` everywhere else
+
+    """
+    if os_is_windows:
+        return os.path.join(
+            os.environ["APPDATA"],
+            config_dir_name
+        )
+    else:
+        return os.path.join(
+            os.path.expanduser('~'),
+            '.config',
+            config_dir_name
+        )
+
+
+DEFAULT_CONFIG_DIR = get_config_dir()
+
+DEFAULT_CREDENTIALS_FILENAME = os.path.join(
+    DEFAULT_CONFIG_DIR,
+    'credentials.json'
+)
+DEFAULT_AUTHORIZED_USER_FILENAME = os.path.join(
+    DEFAULT_CONFIG_DIR,
+    'authorized_user.json'
+)
+
+
+def _create_installed_app_flow(scopes):
+    return InstalledAppFlow.from_client_secrets_file(
+        DEFAULT_CREDENTIALS_FILENAME,
+        scopes
+    )
+
+
+def local_server_flow(scopes, port=0):
+    flow = _create_installed_app_flow(scopes)
+    return flow.run_local_server(port=port)
+
+
+def console_flow(scopes):
+    flow = _create_installed_app_flow(scopes)
+    return flow.run_console()
+
+
+def load_credentials(filename=DEFAULT_AUTHORIZED_USER_FILENAME):
+    if os.path.exists(filename):
+        return Credentials.from_authorized_user_file(filename)
+
+    return None
+
+
+def store_credentials(
+    creds,
+    filename=DEFAULT_AUTHORIZED_USER_FILENAME,
+    strip='token'
+):
+    with open(filename, 'w') as f:
+        f.write(creds.to_json(strip))
+
+
+def oauth(scopes=DEFAULT_SCOPES, flow=local_server_flow):
+    creds = load_credentials()
+
+    if not creds:
+        creds = flow(scopes=scopes)
+        store_credentials(creds)
+
+    client = Client(auth=creds)
+    return client

setup.py

@@ -43,7 +43,11 @@ def read(filename):
     author_email='[email protected]',
     url='https://github.com/burnash/gspread',
     keywords=['spreadsheets', 'google-spreadsheets'],
-    install_requires=['requests>=2.2.1', 'google-auth'],
+    install_requires=[
+        'requests>=2.2.1',
+        'google-auth>=1.12.0',
+        'google-auth-oauthlib>=0.4.1'
+    ],
     python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*',
     classifiers=[
         "Programming Language :: Python",

test-requirements.txt

@@ -1,5 +1,5 @@
 nose
-requests[security]
 google-auth
+google-auth-oauthlib>=0.4.1
 betamax==0.8.1
 -e git+https://github.com/burnash/betamax-json-body-serializer.git#egg=betamax_json_body_serializer