add HTTP basic authentication check

slapos/promise/plugin/check_http_authentication.py

+from zope.interface import implementer
+from slapos.grid.promise import interface
+from slapos.grid.promise.generic import GenericPromise
+
+import requests
+
+@implementer(interface.IPromise)
+class RunPromise(GenericPromise):
+    def __init__(self, config):
+        super(RunPromise, self).__init__(config)
+        self.setPeriodicity(float(self.getConfig('frequency', 2)))
+
+    def sense(self):
+        """
+        Check basic HTTP authentication for a service. You should
+        probably run check_url_available.py first.
+        """
+        url = self.getConfig('url')
+        username = self.getConfig('username')
+        password = self.getConfig('password')
+
+        try:
+            result = requests.get(url, auth=(username, password))
+        except requests.ConnectionError as _:
+            self.logger.error(
+                'ERROR connection not possible while accessing %r' % url)
+            return
+        except Exception as e:
+            self.logger.error('ERROR %r' % e)
+            return
+
+        credentials = '(%r, %r)' % (username, password)
+        if result.ok:
+            self.logger.info('%r authenticated with %s' % (url, credentials))
+        else:
+            self.logger.error('ERROR could not authenticate %r with %s' % \
+                              (url, credentials))
+
+    def anomaly(self):
+        return self._test(result_count=3, failure_amount=3)