offlineimap.conf: learn to evaluate oauth2 related options

Introduce:
- oauth2_client_id_eval
- oauth2_client_secret_eval
- oauth2_access_token_eval
- oauth2_refresh_token_eval

Github-ref: https://github.com/OfflineIMAP/offlineimap/issues/307
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap.conf

@@ -829,6 +829,10 @@ remoteuser = username
 #
 #oauth2_client_id = YOUR_CLIENT_ID
 #oauth2_client_secret = YOUR_CLIENT_SECRET
+#
+# The return values must be bytes.
+#oauth2_client_id_eval = get_client_id("accountname")
+#oauth2_client_secret_eval = get_client_secret("accountname")
 
 # Specify the refresh token to use for the connection to the mail server.
 # Here's an example of a way to get a refresh token:
@@ -853,6 +857,10 @@ remoteuser = username
 #oauth2_access_token = ACCESS_TOKEN
 #oauth2_request_url = https://accounts.google.com/o/oauth2/token
 #oauth2_refresh_token = REFRESH_TOKEN
+#
+# The return values must be bytes.
+#oauth2_access_token_eval = get_access_token("accountname")
+#oauth2_refresh_token_eval = get_refresh_token("accountname")
 
 ########## Passwords
 

offlineimap/CustomConfig.py

@@ -16,8 +16,8 @@
 
 import os
 import re
-import six
 from sys import exc_info
+import six
 
 try:
     from ConfigParser import SafeConfigParser, Error

offlineimap/repository/IMAP.py

@@ -301,16 +301,32 @@ class IMAPRepository(BaseRepository):
         return self._oauth2_request_url
 
     def getoauth2_refresh_token(self):
-        return self.getconf('oauth2_refresh_token', None)
+        refresh_token = self.getconf('oauth2_refresh_token', None)
+        if refresh_token is None:
+            refresh_token = self.localeval.eval(
+                self.getconf('oauth2_refresh_token_eval', "lambda: None"))
+        return refresh_token
 
     def getoauth2_access_token(self):
-        return self.getconf('oauth2_access_token', None)
+        access_token = self.getconf('oauth2_access_token', None)
+        if access_token is None:
+            access_token = self.localeval.eval(
+                self.getconf('oauth2_access_token_eval', "lambda: None"))
+        return access_token
 
     def getoauth2_client_id(self):
-        return self.getconf('oauth2_client_id', None)
+        client_id = self.getconf('oauth2_client_id', None)
+        if client_id is None:
+            client_id = self.localeval.eval(
+                self.getconf('oauth2_client_id_eval', "lambda: None"))
+        return client_id
 
     def getoauth2_client_secret(self):
-        return self.getconf('oauth2_client_secret', None)
+        client_secret = self.getconf('oauth2_client_secret', None)
+        if client_secret is None:
+            client_secret = self.localeval.eval(
+                self.getconf('oauth2_client_secret_eval', "lambda: None"))
+        return client_secret
 
     def getpreauthtunnel(self):
         return self.getconf('preauthtunnel', None)
@@ -325,8 +341,7 @@ class IMAPRepository(BaseRepository):
         return self.getconfboolean('decodefoldernames', False)
 
     def getidlefolders(self):
-        localeval = self.localeval
-        return localeval.eval(self.getconf('idlefolders', '[]'))
+        return self.localeval.eval(self.getconf('idlefolders', '[]'))
 
     def getmaxconnections(self):
         num1 = len(self.getidlefolders())