Code flow authentication for persistent session. Addresses #2

- Add .githubattributes file to recognize .ipynb files as Python

.githubattributes

@@ -0,0 +1,2 @@
+*.ipynb linguist-language=Python
+

OneDrive_Gaph_tutorial.ipynb

@@ -21,14 +21,19 @@
     "import requests\n",
     "import json\n",
     "import urllib\n",
-    "import os"
+    "import os\n",
+    "from getpass import getpass\n",
+    "import time\n",
+    "from datetime import datetime"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Get Access token"
+    "## Get Access token\n",
+    "\n",
+    "### Token flow authentication"
    ]
   },
   {
@@ -85,7 +90,154 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Looks all right. We have got the access token, and included in the HEADERS. You can print response to see more. "
+    "Looks all right. We have got the access token, and included in the HEADERS. You can print response to see more. Go ahead with OneDrive operations."
+   ]
+  },
+  {
+   "source": [
+    "### Code flow authentication\n",
+    "\n",
+    "Code flow returns both `access_token` and `refresh_token` which can be used to\n",
+    "request new `access_token` and `refresh_token` for persistent session. If you \n",
+    "are using organization account, you might require consent of organization administrator. \n"
+   ],
+   "cell_type": "markdown",
+   "metadata": {}
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Get code\n",
+    "URL = 'https://login.microsoftonline.com/common/oauth2/v2.0/authorize'\n",
+    "client_id = \"362422eb-d9d6-4245-9eca-2be5cf256450\"\n",
+    "permissions = ['offline_access', 'files.readwrite', 'User.Read']\n",
+    "response_type = 'code'\n",
+    "redirect_uri = 'http://localhost:8080/'\n",
+    "scope = ''\n",
+    "for items in range(len(permissions)):\n",
+    "    scope = scope + permissions[items]\n",
+    "    if items < len(permissions)-1:\n",
+    "        scope = scope + '+'\n",
+    "\n",
+    "print('Click over this link ' +URL + '?client_id=' + client_id + '&scope=' + scope + '&response_type=' + response_type+\\\n",
+    "     '&redirect_uri=' + urllib.parse.quote(redirect_uri))\n",
+    "print('Sign in to your account, copy the whole redirected URL.')\n",
+    "code = getpass(\"Paste the URL here :\")\n",
+    "code = code[(code.find('?code') + len('?code') + 1) :]\n",
+    "\n",
+    "URL = 'https://login.microsoftonline.com/common/oauth2/v2.0/token'\n",
+    "\n",
+    "response = requests.post(URL + '?client_id=' + client_id + '&scope=' + scope + '&grant_type=authorization_code' +\\\n",
+    "     '&redirect_uri=' + urllib.parse.quote(redirect_uri)+ '&code=' + code)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Get token\n",
+    "data = {\n",
+    "    \"client_id\": client_id,\n",
+    "    \"scope\": permissions,\n",
+    "    \"code\": code,\n",
+    "    \"redirect_uri\": redirect_uri,\n",
+    "    \"grant_type\": 'authorization_code',\n",
+    "    \"client_secret\": client_secret\n",
+    "}\n",
+    "\n",
+    "response = requests.post(URL, data=data)\n",
+    "\n",
+    "token = json.loads(response.text)[\"access_token\"]\n",
+    "refresh_token = json.loads(response.text)[\"refresh_token\"]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Refresh token\n",
+    "def get_refresh_token():\n",
+    "    data = {\n",
+    "        \"client_id\": client_id,\n",
+    "        \"scope\": permissions,\n",
+    "        \"refresh_token\": refresh_token,\n",
+    "        \"redirect_uri\": redirect_uri,\n",
+    "        \"grant_type\": 'refresh_token',\n",
+    "        \"client_secret\": 'xxxx-yyyy-zzzz',\n",
+    "    }\n",
+    "\n",
+    "    response = requests.post(URL, data=data)\n",
+    "\n",
+    "    token = json.loads(response.text)[\"access_token\"]\n",
+    "    refresh_token = json.loads(response.text)[\"refresh_token\"]\n",
+    "    last_updated = time.mktime(datetime.today().timetuple())\n",
+    "\n",
+    "    return token, refresh_token, last_updated"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "token, refresh_token, last_updated = get_refresh_token()"
+   ]
+  },
+  {
+   "source": [
+    "If you have a large data to upload, you may use below mock code inside your upload loop:\n",
+    "\n",
+    "```python\n",
+    "elapsed_time = time.mktime(datetime.today().timetuple()) - last_updated\n",
+    "\n",
+    "if (elapsed_time < 45*60*60):\n",
+    "    do_something()\n",
+    "else if (elapsed_time < 59*60*60):\n",
+    "    token, refresh_token, last_updated = get_refresh_token()\n",
+    "else:\n",
+    "    go_to_code_flow()\n",
+    "```"
+   ],
+   "cell_type": "markdown",
+   "metadata": {}
+  },
+  {
+   "source": [
+    "## OneDrive operations"
+   ],
+   "cell_type": "markdown",
+   "metadata": {}
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "URL = 'https://graph.microsoft.com/v1.0/'\n",
+    "\n",
+    "HEADERS = {'Authorization': 'Bearer ' + token}\n",
+    "\n",
+    "response = requests.get(URL + 'me/drive/', headers = HEADERS)\n",
+    "if (response.status_code == 200):\n",
+    "    response = json.loads(response.text)\n",
+    "    print('Connected to the OneDrive of', response['owner']['user']['displayName']+' (',response['driveType']+' ).', \\\n",
+    "         '\\nConnection valid for one hour. Refresh token if required.')\n",
+    "elif (response.status_code == 401):\n",
+    "    response = json.loads(response.text)\n",
+    "    print('API Error! : ', response['error']['code'],\\\n",
+    "         '\\nSee response for more details.')\n",
+    "else:\n",
+    "    response = json.loads(response.text)\n",
+    "    print('Unknown error! See response for more details.')"
    ]
   },
   {