improve error message for OAuth2 authentication

gallery_dl/extractor/deviantart.py

@@ -561,10 +561,11 @@ class DeviantartAPI():
 
         auth = (self.client_id, self.client_secret)
         response = self.session.post(url, data=data, auth=auth)
-        if response.status_code != 200:
-            raise exception.AuthenticationError()
-
         data = response.json()
+
+        if response.status_code != 200:
+            raise exception.AuthenticationError('"{} ({})"'.format(
+                data.get("error_description"), data.get("error")))
         if refresh_token:
             _refresh_token_cache.invalidate(refresh_token)
             _refresh_token_cache(refresh_token, data["refresh_token"])

gallery_dl/extractor/reddit.py

@@ -216,7 +216,7 @@ class RedditAPI():
         """Actual authenticate implementation"""
         url = "https://www.reddit.com/api/v1/access_token"
         if refresh_token:
-            self.log.info("Refreshing access token")
+            self.log.info("Refreshing private access token")
             data = {"grant_type": "refresh_token",
                     "refresh_token": refresh_token}
         else:
@@ -226,7 +226,8 @@ class RedditAPI():
                     "device_id": "DO_NOT_TRACK_THIS_DEVICE"}
         response = self.session.post(url, data=data, auth=(self.client_id, ""))
         if response.status_code != 200:
-            raise exception.AuthenticationError()
+            raise exception.AuthenticationError('"{} ({})"'.format(
+                response.json().get("message"), response.status_code))
         return "Bearer " + response.json()["access_token"]
 
     def _call(self, endpoint, params):

gallery_dl/job.py

@@ -63,9 +63,9 @@ class Job():
             log = self.extractor.log
             for msg in self.extractor:
                 self.dispatch(msg)
-        except exception.AuthenticationError:
+        except exception.AuthenticationError as exc:
-            log.error("Authentication failed. Please provide a valid "
+            msg = str(exc) or "Please provide a valid username/password pair."
-                      "username/password pair.")
+            log.error("Authentication failed: %s", msg)
         except exception.AuthorizationError:
             log.error("You do not have permission to access the resource "
                       "at '%s'", self.url)