backends: Report only relevant exceptions to sentry

When catching KeycloakError exceptions, other exception types
will be then raised like ValueError or AuthenticationFailed.

Those will be processed by django applications using these auth
middlewares so there is no need to duplicate error reports in
sentry here.

swh/auth/django/backends.py

-# Copyright (C) 2020-2021  The Software Heritage developers
+# Copyright (C) 2020-2022  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -121,7 +121,8 @@ class OIDCAuthorizationCodePKCEBackend:
                 if error_msg == "invalid_grant: Session not active":
                     # user session no longer active, remove oidc profile from cache
                     cache.delete(cache_key)
-                sentry_sdk.capture_exception(ke)
+                else:
+                    sentry_sdk.capture_exception(ke)
                 return None
             except Exception as e:
                 sentry_sdk.capture_exception(e)
@@ -204,8 +205,7 @@ class OIDCBearerTokenAuthentication(BaseAuthentication):
 
             # create Django user
             user = oidc_user_from_decoded_token(decoded_token, oidc_client.client_id)
-        except UnicodeEncodeError as e:
-            sentry_sdk.capture_exception(e)
+        except UnicodeEncodeError:
             raise ValidationError("Invalid bearer token")
         except KeycloakError as ke:
             error_msg = keycloak_error_message(ke)
@@ -217,10 +217,8 @@ class OIDCBearerTokenAuthentication(BaseAuthentication):
                     "Bearer token expired after a long period of inactivity; "
                     "please generate a new one."
                 )
-            sentry_sdk.capture_exception(ke)
             raise AuthenticationFailed(error_msg)
         except Exception as e:
-            sentry_sdk.capture_exception(e)
             raise AuthenticationFailed(str(e))
 
         return user, None