[LTI Provider] Added an authentication backend to log in LTI users

This change adds a Django authentication backend which, when installed
will authenticate users based on their LTI identity rather than using
a username/password combination. The authentication method determines
first whether a user with the given username exists and, if so, whether
that user is associated with an LTI identity. It also verifies that
the LTI consumer and user ID passed to the LTI launch match those
stored in the LtiUser table. This will always be the case if the
authentication backend is reached through the LTI code, but it
provides an extra guarantee if the backend is called from elsewhere.

lms/envs/aws.py

@@ -647,6 +647,10 @@ EDXNOTES_INTERNAL_API = ENV_TOKENS.get('EDXNOTES_INTERNAL_API', EDXNOTES_INTERNA
 
 CREDIT_PROVIDER_SECRET_KEYS = AUTH_TOKENS.get("CREDIT_PROVIDER_SECRET_KEYS", {})
 
-
 ############ CERTIFICATE VERIFICATION URL (STATIC FILES) ###########
 ENV_TOKENS.get('CERTIFICATES_STATIC_VERIFY_URL', CERTIFICATES_STATIC_VERIFY_URL)
+
+##################### LTI Provider #####################
+if FEATURES.get('ENABLE_LTI_PROVIDER'):
+    INSTALLED_APPS += ('lti_provider',)
+    AUTHENTICATION_BACKENDS += ('lti_provider.users.LtiBackend', )

lms/envs/common.py

@@ -2543,3 +2543,9 @@ CREDIT_PROVIDER_SECRET_KEYS = {}
 # when a credit provider notifies us that a student has been approved
 # or denied for credit.
 CREDIT_PROVIDER_TIMESTAMP_EXPIRATION = 15 * 60
+
+# Default domain for the e-mail address associated with users who are created
+# via the LTI Provider feature. Note that the generated e-mail addresses are
+# not expected to be active; this setting simply allows administrators to
+# route any messages intended for LTI users to a common domain.
+LTI_USER_EMAIL_DOMAIN = 'lti.example.com'

lms/envs/test.py

@@ -495,3 +495,4 @@ PROFILE_IMAGE_MIN_BYTES = 100
 # Enable the LTI provider feature for testing
 FEATURES['ENABLE_LTI_PROVIDER'] = True
 INSTALLED_APPS += ('lti_provider',)
+AUTHENTICATION_BACKENDS += ('lti_provider.users.LtiBackend',)