write DeviantArt refresh-tokens to cache (#616)

Writing the token is currently disabled by default and must be
enabled with 'extractor.oauth.cache'.

'extractor.deviantart.refresh-token' must be set to '"cache"'
to use the cached token.

gallery_dl/extractor/deviantart.py

@@ -961,11 +961,15 @@ def __init__(self, extractor):
         self.folders = extractor.config("folders", False)
         self.metadata = extractor.extra or extractor.config("metadata", False)
 
-        self.refresh_token = extractor.config("refresh-token")
-        self.client_id = extractor.config("client-id", self.CLIENT_ID)
+        self.client_id = extractor.config(
+            "client-id", self.CLIENT_ID)
         self.client_secret = extractor.config(
             "client-secret", self.CLIENT_SECRET)
 
+        self.refresh_token = extractor.config("refresh-token")
+        if self.refresh_token == "cache":
+            self.refresh_token = "#" + str(self.client_id)
+
         self.log.debug(
             "Using %s API credentials (client-id %s)",
             "default" if self.client_id == self.CLIENT_ID else "custom",

gallery_dl/extractor/oauth.py

@@ -98,7 +98,7 @@ def _oauth1_authorization_flow(
     def _oauth2_authorization_code_grant(
             self, client_id, client_secret, auth_url, token_url,
             scope="read", key="refresh_token", auth=True,
-            message_template=None):
+            message_template=None, cache=None):
         """Perform an OAuth2 authorization code grant"""
 
         state = "gallery-dl_{}_{}".format(
@@ -162,6 +162,11 @@ def _oauth2_authorization_code_grant(
             client_secret=client_secret,
         ))
 
+        # write to cache
+        if cache and config.get(("extractor", self.category), "cache"):
+            cache.update("#" + str(client_id), data[key])
+            self.log.info("Writing 'refresh-token' to cache")
+
 
 class OAuthDeviantart(OAuthBase):
     subcategory = "deviantart"
@@ -179,6 +184,7 @@ def items(self):
             "https://www.deviantart.com/oauth2/authorize",
             "https://www.deviantart.com/oauth2/token",
             scope="browse",
+            cache=deviantart._refresh_token_cache,
         )