fix: prevent setting user attributes from JWT in Studio

Open edX implements its a JwtAuthentication class in edx-drf-extensions
(in edx_rest_framework_extensions.auth.jwt.authentication). This class
updates the local User database entry to match certain values in the
token. It's used as a way to automatically provision and update users
with their LMS user information on other Open edX services like
ecommerce.

Since LMS and Studio keep the record of truth in its database tables,
they should *not* update their database user information based on the
JWT. Doing so would allow stale JWTs to incorrectly reset user values
after they had been changed in the LMS. This is done by having the
EDX_DRF_EXTENSIONS['JWT_PAYLOAD_USER_ATTRIBUTE_MAPPING'] setting be an
empty dictionary, and was set correctly for the LMS in its common.py env
settings module. Unfortunately, this was *not* being set for Studio.

This commit adds the same setting to Studio's common settings module.
Prior to this commit, it was possible for a stale JWT to reset user
attributes if the user hit a Studio API endpoint that used JWT for  auth
(e.g. endpoints used by the Course Authoring MFE). This opened up a
potential security issue where a global staff user (is_staff=True) that
had their global staff status removed (is_staff=False) could have up to
a one hour window in which they could use their stale-but-still-valid
global-staff JWT token to regain global staff status by calling a Studio
endpoint with their browser.

cms/envs/common.py

@@ -2242,7 +2242,6 @@
 
 ############################ OAUTH2 Provider ###################################
 
-
 # 5 minute expiration time for JWT id tokens issued for external API requests.
 OAUTH_ID_TOKEN_EXPIRATION = 5 * 60
 
@@ -2252,6 +2251,12 @@
 # Affiliate cookie tracking
 AFFILIATE_COOKIE_NAME = 'dev_affiliate_id'
 
+EDX_DRF_EXTENSIONS = {
+    # Set this value to an empty dict in order to prevent automatically updating
+    # user data from values in (possibly stale) JWTs.
+    'JWT_PAYLOAD_USER_ATTRIBUTE_MAPPING': {},
+}
+
 ############## Settings for Studio Context Sensitive Help ##############
 
 HELP_TOKENS_INI_FILE = REPO_ROOT / "cms" / "envs" / "help_tokens.ini"