adding comments for OAuth2 token login

src/driver/implementation/imap/imapstorage.h

@@ -69,6 +69,8 @@ extern "C" {
   @param login is the login of the IMAP4rev1 account.
 
   @param password is the password of the IMAP4rev1 account.
+    If performing OAuth2 login, use the OAuth2 token here
+    instead of password.
 
   @param cached if this value is != 0, a persistant cache will be
     stored on local system.

src/driver/interface/maildriver.h

@@ -585,7 +585,7 @@ int mailsession_get_message_by_uid(mailsession * session,
   @param remote_ip_port remote IP:port (server)
   @param login          login
   @param auth_name      authentication name
-  @param password       password
+  @param password       password (or token for OAuth2 login)
   @param realm          realm
 
   @return MAIL_NO_ERROR is returned on success, MAIL_ERROR_XXX is returned