Add SimpleAuth implementation (#106)

* Add SimpleAuth implementation

* Add logic to preserve hadoop.auth

* Always set auth token

* Fix cookies passing

... without losing them from session

* Add default user "yarn"

Author: dimon222

yarn_api_client/auth.py

@@ -0,0 +1,24 @@
+import requests
+
+class SimpleAuth(requests.auth.AuthBase):
+    def __init__(self, username="yarn"):
+        self.username = username
+        self.auth_token = None
+        self.auth_done = False
+
+    def __call__(self, request):
+        if not self.auth_done:
+            _session = requests.Session()
+            r = _session.get(request.url, params={"user.name": self.username})
+            r.raise_for_status()
+            self.auth_token = _session.cookies.get_dict()['hadoop.auth']
+            self.auth_done = True
+
+        # Borrowed from https://github.com/psf/requests/issues/2532#issuecomment-90126896
+        if 'Cookie' in request.headers:
+            old_cookies = request.headers['Cookie']
+            all_cookies = '; '.join([old_cookies, "{0}={1}".format("hadoop.auth", self.auth_token)])
+            request.headers['Cookie'] = all_cookies
+        else:
+            request.prepare_cookies({"hadoop.auth": self.auth_token})
+        return request