# HG changeset patch
# User Kim Alvefur <zash@zash.se>
# Date 1683834009 -7200
# Node ID 9d542e86e19a684bdf1cbc584b88f0d02cf19b35
# Parent  aa4828f040c5db5ec458977e2488797c01cd3132
mod_http_oauth2: Allow requesting a subset of scopes on token refresh

This enables clients to request access tokens with fewer permissions
than the grant they were given, reducing impact of token leak. Clients
could e.g. request access tokens with some privileges and immediately
revoke them after use, or other strategies.

diff -r aa4828f040c5 -r 9d542e86e19a mod_http_oauth2/mod_http_oauth2.lua
--- a/mod_http_oauth2/mod_http_oauth2.lua	Thu May 11 19:33:44 2023 +0200
+++ b/mod_http_oauth2/mod_http_oauth2.lua	Thu May 11 21:40:09 2023 +0200
@@ -411,14 +411,22 @@
 	end
 
 	local refresh_scopes = refresh_token_info.grant.data.oauth2_scopes;
+
+	if params.scope then
+		local granted_scopes = set.new(parse_scopes(refresh_scopes));
+		local requested_scopes = parse_scopes(params.scope);
+		refresh_scopes = array.filter(requested_scopes, function(scope)
+			return granted_scopes:contains(scope);
+		end):concat(" ");
+	end
+
+	local username = jid.split(refresh_token_info.jid);
 	local new_scopes, role = filter_scopes(username, refresh_scopes);
 
 	-- new_access_token() requires the actual token
 	refresh_token_info.token = params.refresh_token;
 
-	return json.encode(new_access_token(
-		refresh_token_info.jid, role, new_scopes, client, nil, refresh_token_info
-	));
+	return json.encode(new_access_token(refresh_token_info.jid, role, new_scopes, client, nil, refresh_token_info));
 end
 
 -- RFC 7636 Proof Key for Code Exchange by OAuth Public Clients