Add common/djangoapps/third_party_auth; update pylintrc to allow test_* names.

third_party_auth contains a working settings mechanism, the start of the provider interface + 3 implementations (Google, Mozilla Persona, LinkedIn), and a stub for the auth pipeline. Modified existing lms settings files to use but deactivate the module.

common/djangoapps/third_party_auth/settings.py

@@ -0,0 +1,106 @@
+"""Settings for the third-party auth module.
+
+Defers configuration of settings so we can inspect the provider registry and
+create settings placeholders for only those values actually needed by a given
+deployment. Required by Django; consequently, this file must not invoke the
+Django armature.
+
+The flow for settings registration is:
+
+The base settings file contains a boolean, ENABLE_THIRD_PARTY_AUTH, indicating
+whether this module is enabled. Ancillary settings files (aws.py, dev.py) put
+options in THIRD_PARTY_SETTINGS. startup.py probes the ENABLE_THIRD_PARTY_AUTH.
+If true, it:
+
+    a) loads this module.
+    b) calls apply_settings(), passing in settings.THIRD_PARTY_AUTH.
+       THIRD_PARTY AUTH is a dict of the form
+
+       'THIRD_PARTY_AUTH': {
+            '<PROVIDER_NAME>': {
+                '<PROVIDER_SETTING_NAME>': '<PROVIDER_SETTING_VALUE>',
+                [...]
+            },
+            [...]
+       }
+
+       If you are using a dev settings file, your settings dict starts at the
+       level of <PROVIDER_NAME> and is a map of provider name string to
+       settings dict. If you are using an auth.json file, it should contain a
+       THIRD_PARTY_AUTH entry as above.
+    c) apply_settings() builds a list of <PROVIDER_NAMES>. These are the
+       enabled third party auth providers for the deployment. These are enabled
+       in provider.Registry, the canonical list of enabled providers.
+    d) then, it sets global, provider-independent settings.
+    e) then, it sets provider-specific settings. For each enabled provider, we
+       read its SETTINGS member. These are merged onto the Django settings
+       object. In most cases these are stubs and the real values are set from
+       THIRD_PARTY_AUTH. All values that are set from this dict must first be
+       initialized from SETTINGS. This allows us to validate the dict and
+       ensure that the values match expected configuration options on the
+       provider.
+    f) finally, the (key, value) pairs from the dict file are merged onto the
+       django settings object.
+"""
+
+from . import provider
+
+
+def _merge_auth_info(django_settings, auth_info):
+    """Merge `auth_info` dict onto `django_settings` module."""
+    enabled_provider_names = []
+    to_merge = []
+
+    for provider_name, provider_dict in auth_info.items():
+        enabled_provider_names.append(provider_name)
+        # Merge iff all settings have been intialized.
+        for key in provider_dict:
+            if key not in dir(django_settings):
+                raise ValueError('Auth setting %s not initialized' % key)
+        to_merge.append(provider_dict)
+
+    for passed_validation in to_merge:
+        for key, value in passed_validation.iteritems():
+            setattr(django_settings, key, value)
+
+
+def _set_global_settings(django_settings):
+    """Set provider-independent settings."""
+    # Register and configure python-social-auth with Django.
+    django_settings.INSTALLED_APPS += (
+        'social.apps.django_app.default',
+        'third_party_auth',
+    )
+    django_settings.TEMPLATE_CONTEXT_PROCESSORS += (
+        'social.apps.django_app.context_processors.backends',
+        'social.apps.django_app.context_processors.login_redirect',
+    )
+    # Inject our customized auth pipeline. All auth backends must work with
+    # this pipeline.
+    django_settings.SOCIAL_AUTH_PIPELINE = (
+        'third_party_auth.pipeline.step',
+    )
+
+
+def _set_provider_settings(django_settings, enabled_providers, auth_info):
+    """Set provider-specific settings."""
+    # Must prepend here so we get called first.
+    django_settings.AUTHENTICATION_BACKENDS = (
+        tuple(enabled_provider.AUTHENTICATION_BACKEND for enabled_provider in enabled_providers) +
+        django_settings.AUTHENTICATION_BACKENDS)
+
+    # Merge settings from provider classes, and configure all placeholders.
+    for enabled_provider in enabled_providers:
+        enabled_provider.merge_onto(django_settings)
+
+    # Merge settings from <deployment>.auth.json.
+    _merge_auth_info(django_settings, auth_info)
+
+
+def apply_settings(auth_info, django_settings):
+    """Apply settings from `auth_info` dict to `django_settings` module."""
+    provider_names = auth_info.keys()
+    provider.Registry.configure_once(provider_names)
+    enabled_providers = provider.Registry.enabled()
+    _set_global_settings(django_settings)
+    _set_provider_settings(django_settings, enabled_providers, auth_info)